Công Nghệ File

There are two common classes used for reading from a text file. they are:

Programming simple I/O operations is easy, which involves only a few classes and methods. You could do it by looking at a few samples. Programming efficient, portable I/O is extremely difficult, especially if you have to deal with different character sets. This explains why there are so many I/O packages [nine in JDK 1.7]!

JDK has two sets of I/O packages:

the Standard I/O [in package
```
public void abstract void write[int unsignedByte] throws IOException
```
5], introduced since JDK 1.0 for stream-based I/O, and
the New I/O [in packages
```
public void abstract void write[int unsignedByte] throws IOException
```
6], introduced in JDK 1.4, for more efficient buffer-based I/O.

JDK 1.5 introduces the formatted text-I/O via new classes

public void abstract void write[int unsignedByte] throws IOException

7 and

public void abstract void write[int unsignedByte] throws IOException

8, and C-like

public void abstract void write[int unsignedByte] throws IOException

9 and

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

0 methods for formatted output using format specifiers.

JDK 1.7 enhances supports for file I/O via the so-called NIO.2 [non-blocking I/O] in new package

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

1 and its auxiliary packages. It also introduces a new

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

2-with-resources syntax to simplify the coding of

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

3 method.

File and Directory

Class

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

4 [Pre-JDK 7]

The class

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

4 can represent either a file or a directory. [JDK 1.7 introduces a more versatile

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

6, which overcomes many limitations of

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

4.]

A path string is used to locate a file or a directory. Unfortunately, path strings are system dependent, e.g., "

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

8" in Windows or "

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

9" in Unix/Mac.

Windows use back-slash

File size is 417455 bytes
Elapsed Time is 2.938921 msec

0 as the directory separator; while Unixes/Mac use forward-slash

File size is 417455 bytes
Elapsed Time is 2.938921 msec

Windows use semi-colon

File size is 417455 bytes
Elapsed Time is 2.938921 msec

2 as path separator to separate a list of paths; while Unixes/Mac use colon

File size is 417455 bytes
Elapsed Time is 2.938921 msec

Windows use "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

4" as line delimiter for text file; while Unixes use "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

5" and Mac uses "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

6".

The "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

7" or "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

8" is called the root. Windows supports multiple roots, each maps to a drive [e.g., "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

7", "

File size is 417455 bytes
Elapsed Time is 61.834954 msec

0"]. Unixes/Mac has a single root ["

File size is 417455 bytes
Elapsed Time is 2.938921 msec

8"].

A path could be absolute [beginning from the root] or relative [which is relative to a reference directory]. Special notations "

File size is 417455 bytes
Elapsed Time is 61.834954 msec

2" and "

File size is 417455 bytes
Elapsed Time is 61.834954 msec

3" denote the current directory and the parent directory, respectively.

The

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

4 class maintains these system-dependent properties, for you to write programs that are portable:

Directory Separator: in

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 fields

File size is 417455 bytes
Elapsed Time is 61.834954 msec

6 [as

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7] and

File size is 417455 bytes
Elapsed Time is 61.834954 msec

8. [They failed to follow the Java naming convention for constants adopted since JDK 1.2.] As mentioned, Windows use backslash

File size is 417455 bytes
Elapsed Time is 2.938921 msec

0; while Unixes/Mac use forward slash

File size is 417455 bytes
Elapsed Time is 2.938921 msec

Path Separator: in

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 fields

DataInputStream in = new DataInputStream[
                        new BufferedInputStream[
                           new FileInputStream["in.dat"]]];

2 [as

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7] and

DataInputStream in = new DataInputStream[
                        new BufferedInputStream[
                           new FileInputStream["in.dat"]]];

4. As mentioned, Windows use semi-colon

File size is 417455 bytes
Elapsed Time is 2.938921 msec

2 to separate a list of paths; while Unixes/Mac use colon

File size is 417455 bytes
Elapsed Time is 2.938921 msec

You can construct a

DataInputStream in = new DataInputStream[
                        new BufferedInputStream[
                           new FileInputStream["in.dat"]]];

7 instance with a path string or URI, as follows. Take note that the physical file/directory may or may not exist. A file URL takes the form of

DataInputStream in = new DataInputStream[
                        new BufferedInputStream[
                           new FileInputStream["in.dat"]]];

8, e.g.,

DataInputStream in = new DataInputStream[
                        new BufferedInputStream[
                           new FileInputStream["in.dat"]]];

For examples,

For applications that you intend to distribute as JAR files, you should use the

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

0 class to reference the resources, as it can reference disk files as well as JAR'ed files , for example,

java.net.URL url = this.getClass[].getResource["icon.png"];

Verifying Properties of a File/DirectoryList Directory

For a directory, you can use the following methods to list its contents:

Example: The following program recursively lists the contents of a given directory [similar to Unix's

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

1 command].

[Advanced] List Directory with Filter

You can apply a filter to

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

2 and

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

3, to list only files that meet a certain criteria.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

The

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

5 declares one

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 method:

public boolean accept[File dirName, String fileName]

The

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

2 and

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

3 methods does a call-back to

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

9 for each of the file/sub-directory produced. You can program your filtering criteria in

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

9. Those files/sub-directories that result in a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

01 return will be excluded.

Example: The following program lists only files that meet a certain filtering criteria.

Class

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

6 [JDK 7]

Read "".

Stream I/O in Standard I/O [java.io Package]

Programs read inputs from data sources [e.g., keyboard, file, network, memory buffer, or another program] and write outputs to data sinks [e.g., display console, file, network, memory buffer, or another program]. In Java standard I/O, inputs and outputs are handled by the so-called streams. A stream is a sequential and contiguous one-way flow of data [just like water or oil flows through the pipe]. It is important to mention that Java does not differentiate between the various types of data sources or sinks [e.g., file or network] in stream I/O. They are all treated as a sequential flow of data. Input and output streams can be established from/to any data source/sink, such as files, network, keyboard/console or another program. The Java program receives data from a source by opening an input stream, and sends data to a sink by opening an output stream. All Java I/O streams are one-way [except the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

03, which will be discussed later]. If your program needs to perform both input and output, you have to open two streams - an input stream and an output stream.

Stream I/O operations involve three steps:

Open an input/output stream associated with a physical device [e.g., file, network, console/keyboard], by constructing an appropriate I/O stream instance.
Read from the opened input stream until "end-of-stream" encountered, or write to the opened output stream [and optionally flush the buffered output].
Close the input/output stream.

Java's I/O operations is more complicated than C/C++ to support internationalization [i18n]. Java internally stores characters [

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

04 type] in 16-bit UCS-2 character set. But the external data source/sink could store characters in other character set [e.g., US-ASCII, ISO-8859-x, UTF-8, UTF-16, and many others], in fixed length of 8-bit or 16-bit, or in variable length of 1 to 4 bytes. [Read ""]. As a consequence, Java needs to differentiate between byte-based I/O for processing raw bytes or binary data, and character-based I/O for processing texts made up of characters.

Byte-Based I/O & Byte Streams

Byte streams are used to read/write raw bytes serially from/to an external device. All the byte streams are derived from the

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 superclasses

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07, as illustrated in the class diagram.

Reading from an InputStream

The

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 superclass

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 declares an

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 method

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11 to read one data-byte from the input source:

public abstract int read[] throws IOException

The

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11 method:

returns the input byte read as an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13 in the range of 0 to 255, or

returns -1 if "end of stream" condition is detected, or

throws an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

14 if it encounters an I/O error.

The

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11 method returns an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13 instead of a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

17, because it uses -1 to indicate end-of-stream.

The

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11 method blocks until a byte is available, an I/O error occurs, or the "end-of-stream" is detected. The term "block" means that the method [and the program] will be suspended. The program will resume only when the method returns.

Two variations of

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11 methods are implemented in the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 for reading a block of bytes into a byte-array. It returns the number of bytes read, or -1 if "end-of-stream" encounters.

Writing to an OutputStream

Similar to the input counterpart, the

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 superclass

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07 declares an abstract method

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

23 to write a data-byte to the output sink.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

23 takes an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13. The least-significant byte of the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13 argument is written out; the upper 3 bytes are discarded. It throws an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

14 if I/O error occurs [e.g., output stream has been closed].

public void abstract void write[int unsignedByte] throws IOException

Similar to the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11, two variations of the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

23 method to write a block of bytes from a byte-array are implemented:

Opening & Closing I/O Streams

You open an I/O stream by constructing an instance of the stream. Both the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 and the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07 provides a

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

3 method to close the stream, which performs the necessary clean-up operations to free up the system resources.

It is a good practice to explicitly close the I/O stream, by running

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

3 in the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

34 clause of

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

35 to free up the system resources immediately when the stream is no longer needed. This could prevent serious resource leaks. Unfortunately, the

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

3 method also throws a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

14, and needs to be enclosed in a nested

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

38 statement, as follows. This makes the codes somehow ugly.

JDK 1.7 introduces a new

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

2-with-resources syntax, which automatically closes all the opened resources after

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

2 or

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

41, as follows. This produces much neater codes.

Flushing the OutputStream

In addition, the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07 provides a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

43 method to flush the remaining bytes from the output buffer.

Implementations of abstract InputStream/OutputStream

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07 are

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 classes that cannot be instantiated. You need to choose an appropriate concrete subclass to establish a connection to a physical device. For example, you can instantiate a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

47 or

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

48 to establish a stream to a physical disk file.

Layered [or Chained] I/O Streams

The I/O streams are often layered or chained with other I/O streams, for purposes such as buffering, filtering, or data-format conversion [between raw bytes and primitive types]. For example, we can layer a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

49 to a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

47 for buffered input, and stack a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

51 in front for formatted data input [using primitives such as

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13,

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

53], as illustrated in the following diagrams.

File I/O Byte-Streams - FileInputStream & FileOutputStream

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

47 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

48 are concrete implementations to the

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 classes

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07, to support I/O from disk files.

Buffered I/O Byte-Streams - BufferedInputStream & BufferedOutputStream

The

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11/

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

23 method in

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06/

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07 are designed to read/write a single byte of data on each call. This is grossly inefficient, as each call is handled by the underlying operating system [which may trigger a disk access, or other expensive operations]. Buffering, which reads/writes a block of bytes from the external device into/from a memory buffer in a single I/O operation, is commonly applied to speed up the I/O.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

47/

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

48 is not buffered. It is often chained to a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

49 or

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

66, which provides the buffering. To chain the streams together, simply pass an instance of one stream into the constructor of another stream. For example, the following codes chain a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

47 to a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

49, and finally, a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

51:

Example 1: Copying a file byte-by-byte without Buffering.

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

This example copies a file by reading a byte from the input file and writing it to the output file. It uses

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

47 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

48 directly without buffering. Notice that most the I/O methods "throws"

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

14, which must be caught or declared to be thrown. The method

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

3 is programmed inside the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

34 clause. It is guaranteed to be run after

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

2 or

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

41. However, method

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

3 also throws an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

14, and therefore must be enclosed inside a nested

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

38 block, which makes the codes a little ugly.

I used

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

80, which was introduced in JDK 1.5, for a more accurate measure of the elapsed time, instead of the legacy not-so-precise

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

81. The output shows that it took about 4 seconds to copy a 400KB file.

As mentioned, JDK 1.7 introduces a new

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

2-with-resources syntax, which automatically closes all the resources opened, after

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

2 or

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

41. For example, the above example can be re-written in a much neater manner as follow:

Example 2: Copying a file with a Programmer-Managed Buffer.

File size is 417455 bytes
Elapsed Time is 2.938921 msec

This example again uses

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

47 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

48 directly. However, instead of reading/writing one byte at a time, it reads/writes a 4KB block. This program took only 3 millisecond - a more than 1000 times speed-up compared with the previous example.

Larger buffer size, up to a certain limit, generally improves the I/O performance. However, there is a trade-off between speed-up the the memory usage. For file copying, a large buffer is certainly recommended. But for reading just a few bytes from a file, large buffer simply wastes the memory.

I re-write the program using JDK 1.7, and try on various buffer size on a much bigger file of 26MB.

Increasing buffer size helps only up to a certain point?!

Example 3: Copying a file with Buffered Streams.

File size is 417455 bytes
Elapsed Time is 61.834954 msec

In this example, I chain the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

47 with

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

49,

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

48 with

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

66, and read/write byte-by-byte. The JRE decides on the buffer size. The program took 62 milliseconds, about 60 times speed-up compared with example 1, but slower than the programmer-managed buffer.

The JDK 1.7 version of the above example is as follows:

Formatted Data-Streams: DataInputStream & DataOutputStream

The

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

51 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

92 can be stacked on top of any

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07 to parse the raw bytes so as to perform I/O operations in the desired data format, such as

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

53.

To use

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

51 for formatted input, you can chain up the input streams as follows:

DataInputStream in = new DataInputStream[
                        new BufferedInputStream[
                           new FileInputStream["in.dat"]]];

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

51 implements

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

99 interface, which provides methods to read formatted primitive data and

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7, such as:

Similarly, you can stack the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

92 as follows:

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

92 implements

public boolean accept[File dirName, String fileName]

03 interface, which provides methods to write formatted primitive data and

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7. For examples,

Example: The following program writes some primitives to a disk file. It then reads the raw bytes to check how the primitives were stored. Finally, it reads the data as primitives.

The data stored in the disk are exactly in the same form as in the Java program internally [e.g., UCS-2 for characters]. The byte-order is big-endian [big byte first, or most significant byte in lowest address].

Network I/O

[In Java Networking]

Character-Based I/O & Character Streams

Java internally stores characters [

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

04 type] in 16-bit UCS-2 character set. But the external data source/sink could store characters in other character set [e.g., US-ASCII, ISO-8859-x, UTF-8, UTF-16, and many others], in fixed length of 8-bit or 16-bit, or in variable length of 1 to 4 bytes. [Read ""]. Hence, Java has to differentiate between byte-based I/O for processing 8-bit raw bytes, and character-based I/O for processing texts. The character streams needs to translate between the character set used by external I/O devices and Java internal UCS-2 format. For example, the character '您' is stored as "

public boolean accept[File dirName, String fileName]

06" in UCS-2 [Java internal], "

public boolean accept[File dirName, String fileName]

07" in UTF8, "

public boolean accept[File dirName, String fileName]

08" in GBK/GB2312, and "

public boolean accept[File dirName, String fileName]

09" in BIG5. If this character is to be written to a file uses UTF-8, the character stream needs to translate "

public boolean accept[File dirName, String fileName]

06" to "

public boolean accept[File dirName, String fileName]

07". The reserve takes place in a reading operation.

The byte/character streams refer to the unit of operation within the Java programs, which does not necessary correspond to the amount of data transferred from/to the external I/O devices. This is because some charsets use fixed-length of 8-bit [e.g., US-ASCII, ISO-8859-1] or 16-bit [e.g., UCS-16], while some use variable-length of 1-4 bytes [e.g., UTF-8, UTF-16, UTF-16-BE, UTF-16-LE, GBK, BIG5]. When a character stream is used to read an 8-bit ASCII file, an 8-bit data is read from the file and put into the 16-bit

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

04 location of the Java program.

Abstract superclass Reader and Writer

Other than the unit of operation and charset conversion [which is extremely complex], character-based I/O is almost identical to byte-based I/O. Instead of

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07, we use

public boolean accept[File dirName, String fileName]

15 and

public boolean accept[File dirName, String fileName]

16 for character-based I/O.

The

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 superclass

public boolean accept[File dirName, String fileName]

15 operates on

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

04. It declares an

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 method

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11 to read one character from the input source.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11 returns the character as an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13 between 0 to 65535 [a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

04 in Java can be treated as an unsigned 16-bit integer]; or -1 if end-of-stream is detected; or throws an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

14 if I/O error occurs. There are also two variations of

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11 to read a block of characters into

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

04-array.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

The

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 superclass

public boolean accept[File dirName, String fileName]

16 declares an

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 method

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

23, which writes a character to the output sink. The lower 2 bytes of the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13 argument is written out; while the upper 2 bytes are discarded.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

File I/O Character-Streams - FileReader & FileWriter

public boolean accept[File dirName, String fileName]

33 and

public boolean accept[File dirName, String fileName]

34 are concrete implementations to the

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 superclasses

public boolean accept[File dirName, String fileName]

15 and

public boolean accept[File dirName, String fileName]

16, to support I/O from disk files.

public boolean accept[File dirName, String fileName]

33/

public boolean accept[File dirName, String fileName]

34 assumes that the default character encoding [charset] is used for the disk file. The default charset is kept in the JVM's system property "

public boolean accept[File dirName, String fileName]

40". You can get the default charset via

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 method

public boolean accept[File dirName, String fileName]

42 or

public boolean accept[File dirName, String fileName]

43. It is probable safe to use

public boolean accept[File dirName, String fileName]

33/

public boolean accept[File dirName, String fileName]

34 for ASCII texts, provided that the default charset is compatible to ASCII [such as US-ASCII, ISO-8859-x, UTF-8, and many others, but NOT UTF-16, UTF-16BE, UTF-16LE and many others]. Use of

public boolean accept[File dirName, String fileName]

46 is NOT recommended as you have no control of the file encoding charset.

Buffered I/O Character-Streams - BufferedReader & BufferedWriter

public boolean accept[File dirName, String fileName]

47 and

public boolean accept[File dirName, String fileName]

48 can be stacked on top of

public boolean accept[File dirName, String fileName]

46 or other character streams to perform buffered I/O, instead of character-by-character.

public boolean accept[File dirName, String fileName]

47 provides a new method

public boolean accept[File dirName, String fileName]

51, which reads a line and returns a

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7 [without the line delimiter]. Lines could be delimited by "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

5" [Unix], "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

4" [Windows], or "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

6" [Mac].

Example

Character Set [or Charset] - Package java.nio.charset [JDK 1.4]

JDK 1.4 provides a new package

public boolean accept[File dirName, String fileName]

56 as part of NIO [New IO] to support character translation between the Unicode [UCS-2] used internally in Java program and external devices which could be encoded in any other format [e.g., US-ASCII, ISO-8859-x, UTF-8, UTF-16, UTF-16BE, UTF-16LE, and etc.]

The main class

public boolean accept[File dirName, String fileName]

57 provides

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 methods for testing whether a particular charset is supported, locating charset instances by name, and listing all the available charsets and the default charset.

Example

The default charset for file encoding is kept in the system property "

public boolean accept[File dirName, String fileName]

40". To change the JVM's default charset for file encoding, you can use command-line VM option "

public boolean accept[File dirName, String fileName]

60". For example, the following command run the program with default charset of UTF-8.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

Most importantly, the

public boolean accept[File dirName, String fileName]

61 class provides methods to encode/decode characters from UCS-2 used in Java program and the specific charset used in the external devices [such as UTF-8].

The

public boolean accept[File dirName, String fileName]

62/

public boolean accept[File dirName, String fileName]

63 methods operate on

public boolean accept[File dirName, String fileName]

64 and

public boolean accept[File dirName, String fileName]

65 introduced also in JDK 1.4, which will be explain in the New I/O section.

Example: The following example encodes some Unicode texts in various encoding scheme, and display the Hex codes of the encoded byte sequences.

Example: The following example tries out the encoding/decoding on

public boolean accept[File dirName, String fileName]

65 and

public boolean accept[File dirName, String fileName]

64. Buffers will be discussed later under New I/O.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

Text File I/O - InputStreamReader and OutputStreamWriter

As mentioned, Java internally stores characters [

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

public boolean accept[File dirName, String fileName]

33/

public boolean accept[File dirName, String fileName]

34 introduced earlier uses the default charset for decoding/encoding, resulted in non-portable programs.

To choose the charset, you need to use

public boolean accept[File dirName, String fileName]

71 and

public boolean accept[File dirName, String fileName]

72.

public boolean accept[File dirName, String fileName]

71 and

public boolean accept[File dirName, String fileName]

72 are considered to be byte-to-character "bridge" streams.

You can choose the character set in the

public boolean accept[File dirName, String fileName]

71's constructor:

You can list the available charsets via

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 method

public boolean accept[File dirName, String fileName]

77. The commonly-used

public boolean accept[File dirName, String fileName]

61 names supported by Java are:

public boolean accept[File dirName, String fileName]

79": 7-bit ASCII [aka ISO646-US]

public boolean accept[File dirName, String fileName]

80": Latin-1

public boolean accept[File dirName, String fileName]

81": Most commonly-used encoding scheme for Unicode

"
```
public boolean accept[File dirName, String fileName]
```
82": Big-endian [big byte first] [big-endian is usually the default]

public boolean accept[File dirName, String fileName]

83": Little-endian [little byte first]

"
```
public boolean accept[File dirName, String fileName]
```
84": with a 2-byte BOM [Byte-Order-Mark] to specify the byte order. FE FF indicates big-endian, FF FE indicates little-endian.

As the

public boolean accept[File dirName, String fileName]

71/

public boolean accept[File dirName, String fileName]

72 often needs to read/write in multiple bytes, it is best to wrap it with a

public boolean accept[File dirName, String fileName]

47/

public boolean accept[File dirName, String fileName]

48.

Example: The following program writes Unicode texts to a disk file using various charsets for file encoding. It then reads the file byte-by-byte [via a byte-based input stream] to check the encoded characters in the various charsets. Finally, it reads the file using the character-based reader.

As seen from the output, the characters 您好 is encoded differently in different charsets. Nonetheless, the

public boolean accept[File dirName, String fileName]

71 is able to translate the characters into the same UCS-2 used in Java program.

java.io.PrintStream & java.io.PrintWriter

The byte-based

public boolean accept[File dirName, String fileName]

90 supports convenient printing methods such as

public boolean accept[File dirName, String fileName]

91 and

public boolean accept[File dirName, String fileName]

92 for printing primitives and text string. Primitives are converted to their string representation for printing. The

public void abstract void write[int unsignedByte] throws IOException

9 and

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

0 were introduced in JDK 1.5 for formatting output with former specifiers.

public void abstract void write[int unsignedByte] throws IOException

9 and

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

0 are identical.

public boolean accept[File dirName, String fileName]

97 never throws an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

14. Instead, it sets an internal flag which can be checked via the

public boolean accept[File dirName, String fileName]

99 method. A

public boolean accept[File dirName, String fileName]

97 can also be created to flush the output automatically. That is, the

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

43 method is automatically invoked after a byte array is written, one of the

public abstract int read[] throws IOException

02] methods is invoked, or after a newline [

public abstract int read[] throws IOException

03] is written.

The standard output and error streams [

public abstract int read[] throws IOException

04 and

public abstract int read[] throws IOException

05] belong to

public boolean accept[File dirName, String fileName]

97.

All characters printed by a

public boolean accept[File dirName, String fileName]

97 are converted into bytes using the default character encoding. The

public abstract int read[] throws IOException

08 class should be used in situations that require writing characters rather than bytes.

The character-stream

public abstract int read[] throws IOException

08 is similar to

public boolean accept[File dirName, String fileName]

97, except that it write in characters instead of bytes. The

public abstract int read[] throws IOException

08 also supports all the convenient printing methods

public boolean accept[File dirName, String fileName]

91,

public boolean accept[File dirName, String fileName]

92,

public void abstract void write[int unsignedByte] throws IOException

9 and

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

0. It never throws an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

14 and can optionally be created to support automatic flushing.

[TODO] Example to show the difference between

public boolean accept[File dirName, String fileName]

97 and

public abstract int read[] throws IOException

08.

Object Serialization and Object Streams

Data streams [

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

51 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

92] allow you to read and write primitive data [such as

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13,

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

53] and

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7, rather than individual bytes. Object streams [

public abstract int read[] throws IOException

24 and

public abstract int read[] throws IOException

25] go one step further to allow you to read and write entire objects [such as

public abstract int read[] throws IOException

26,

public abstract int read[] throws IOException

27 or any custom objects].

Object serialization is the process of representing a "particular state of an object" in a serialized bit-stream, so that the bit stream can be written out to an external device [such as a disk file or network]. The bit-stream can later be re-constructed to recover the state of that object. Object serialization is necessary to save a state of an object into a disk file for persistence or sent the object across the network for applications such as Web Services, Distributed-object applications, and Remote Method Invocation [RMI].

In Java, object that requires to be serialized must implement

public abstract int read[] throws IOException

28 or

public abstract int read[] throws IOException

29 interface.

public abstract int read[] throws IOException

30 interface is an empty interface [or tagged interface] with nothing declared. Its purpose is simply to declare that particular object is serializable.

ObjectInputStream & ObjectOutputStream

The

public abstract int read[] throws IOException

24 and

public abstract int read[] throws IOException

25 can be used to serialize an object into a bit-stream and transfer it to/from an I/O streams, via these methods:

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

public abstract int read[] throws IOException

24 and

public abstract int read[] throws IOException

25 must be stacked on top of a concrete implementation of

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 or

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07, such as

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

47 or

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

48.

For example, the following code segment writes objects to a disk file. The "

public abstract int read[] throws IOException

39" is the convention for serialized object file type.

To read and re-construct the object back in a program, use the method

public abstract int read[] throws IOException

40, which returns an

public abstract int read[] throws IOException

41. Downcast the

public abstract int read[] throws IOException

42 back to its original type.

Example: Object serialization

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

[Check out these bytes!]

Primitive types and array are, by default, serializable.

The

public abstract int read[] throws IOException

24 and

public abstract int read[] throws IOException

25 implement

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

99 and

public boolean accept[File dirName, String fileName]

03 interface respectively. You can used methods such as

public abstract int read[] throws IOException

47,

public abstract int read[] throws IOException

48,

public abstract int read[] throws IOException

49,

public abstract int read[] throws IOException

50 for reading and writing primitive types.

transient & static

```
File size is 417455 bytes
Elapsed Time is 61.834954 msec
```
5 fields are not serialized, as it belongs to the class instead of the particular instance to be serialized.
To prevent certain fields from being serialized, mark them using the keyword
```
public abstract int read[] throws IOException
```
52. This could cut down the amount of data traffic.

The

public abstract int read[] throws IOException

53 method writes out the class of the object, the class signature, and values of non-

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 and non-

public abstract int read[] throws IOException

52 fields.

java.io.Serializable & Externalizable Interfaces

When you create a class that might be serialized, the class must implement

public abstract int read[] throws IOException

28 interface. The

public abstract int read[] throws IOException

30 interface doesn't declare any methods. Empty interfaces such as

public abstract int read[] throws IOException

30 are known as tagging interfaces. They identify implementing classes as having certain properties, without requiring those classes to actually implement any methods.

Most of the core Java classes implement

public abstract int read[] throws IOException

30, such as all the wrapper classes, collection classes, and GUI classes. In fact, the only core Java classes that do not implement

public abstract int read[] throws IOException

30 are ones that should not be serialized. Arrays of primitives or serializable objects are themselves serializable.

Warning Message "The serialization class does not declare a static final serialVersionUID field of type long" [Advanced]

This warning message is triggered because your class [such as

public abstract int read[] throws IOException

61] implements the

public abstract int read[] throws IOException

28 interface. This interface enables the object to be written out to an output stream serially [via method

public abstract int read[] throws IOException

53]; and read back into the program [via method

public abstract int read[] throws IOException

40]. The serialization runtime uses a number [called

public abstract int read[] throws IOException

65] to ensure that the object read into the program [during deserialization] is compatible with the class definition, and not belonging to another version. It throws an

public abstract int read[] throws IOException

66 otherwise.

You have these options:

Simply ignore this warning message. If a
```
public abstract int read[] throws IOException
```
67 class does not explicitly declare a
```
public abstract int read[] throws IOException
```
65, then the serialization runtime will calculate a default
```
public abstract int read[] throws IOException
```
65 value for that class based on various aspects of the class.

Add a

public abstract int read[] throws IOException

65 [Recommended], e.g.

Suppress this particular warning via annotation

public abstract int read[] throws IOException

71 [in package

public abstract int read[] throws IOException

72] [JDK 1.5]:

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

java.io.Externalizable Interface

The

public abstract int read[] throws IOException

30 has a sub-interface called

public abstract int read[] throws IOException

74, which you could used if you want to customize the way a class is serialized. Since

public abstract int read[] throws IOException

74 extends

public abstract int read[] throws IOException

30, it is also a

public abstract int read[] throws IOException

30 and you could invoke

public abstract int read[] throws IOException

40 and

public abstract int read[] throws IOException

53.

public abstract int read[] throws IOException

74 declares two

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 methods:

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

public abstract int read[] throws IOException

82 and

public abstract int read[] throws IOException

83 are interfaces that are implemented by

public abstract int read[] throws IOException

25 and

public abstract int read[] throws IOException

24, which define the

public abstract int read[] throws IOException

53 and

public abstract int read[] throws IOException

40 methods, respectively. When an instance of

public abstract int read[] throws IOException

74 is passed to an

public abstract int read[] throws IOException

25, the default serialization procedure is bypassed; instead, the stream calls the instance's

public abstract int read[] throws IOException

90 method. Similarly, when an

public abstract int read[] throws IOException

24 reads a

public abstract int read[] throws IOException

92 instance, it uses

public abstract int read[] throws IOException

93 to reconstruct the instance.

public abstract int read[] throws IOException

74 is useful if you want complete control on how your objects shall be serialized/deserialized. For example, you could encrypt sensitive data before the object is serialized.

Random Access Files

All the I/O streams covered so far are one-way streams. That is, they are either read-only input stream or write-only output stream. Furthermore, they are all sequential-access [or serial] streams, meant for reading and writing data sequentially. Nonetheless, it is sometimes necessary to read a file record directly as well as modifying existing records or inserting new records. The class

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

03 provides supports for non-sequential, direct [or random] access to a disk file.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

03 is a two-way stream, supporting both input and output operations in the same stream.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

03 can be treated as a huge byte array. You can use a file pointer [of type

public abstract int read[] throws IOException

98], similar to array index, to access individual byte or group of bytes in primitive types [such as int and double]. The file pointer is located at 0 when the file is opened. It advances automatically for every read and write operation by the number of bytes processed.

In constructing a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

03, you can use flags

public void abstract void write[int unsignedByte] throws IOException

00 or

public void abstract void write[int unsignedByte] throws IOException

01 to indicate whether the file is "read-only" or "read-write" access, e.g.,

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

The following methods are available:

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

03 does not inherit from

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 or

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07. However, it implements

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

99 and

public boolean accept[File dirName, String fileName]

03 interfaces [similar to

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

51 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

92]. Therefore, you can use various methods to read/write primitive types to the file, e.g.,

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

Example: Read and write records from a

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

03. [A student file consists of student record of name [

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7] and id [

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13]].

[PENDING]

Compressed I/O Streams

The classes

public void abstract void write[int unsignedByte] throws IOException

12 and

public void abstract void write[int unsignedByte] throws IOException

13 [in package

public void abstract void write[int unsignedByte] throws IOException

14] support reading and writing of compressed data in ZIP format. The classes

public void abstract void write[int unsignedByte] throws IOException

15 and

public void abstract void write[int unsignedByte] throws IOException

16 [in package

public void abstract void write[int unsignedByte] throws IOException

14] support reading and writing of compressed data in GZIP format.

Example: Reading and writing ZIP files

[@PENDING]

Example: Reading and writing JAR files

[@PENDING]

Formatted Text I/O - java.util.Scanner & java.util.Formatter [JDK 1.5]

Formatted-Text Input via java.util.Scanner

JDK 1.5 introduces

public void abstract void write[int unsignedByte] throws IOException

7 class, which greatly simplifies formatted text input from input source [e.g., files, keyboard, network].

public void abstract void write[int unsignedByte] throws IOException

19, as the name implied, is a simple text scanner which can parse the input text into primitive types and strings using regular expressions. It first breaks the text input into tokens using a delimiter pattern, which is by default the white spaces [blank, tab and newline]. The tokens may then be converted into primitive values of different types using the various

public void abstract void write[int unsignedByte] throws IOException

20 methods [

public void abstract void write[int unsignedByte] throws IOException

21,

public void abstract void write[int unsignedByte] throws IOException

22,

public void abstract void write[int unsignedByte] throws IOException

23,

public void abstract void write[int unsignedByte] throws IOException

24,

public void abstract void write[int unsignedByte] throws IOException

25,

public void abstract void write[int unsignedByte] throws IOException

26,

public void abstract void write[int unsignedByte] throws IOException

27,

public void abstract void write[int unsignedByte] throws IOException

28 for

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7, and

public void abstract void write[int unsignedByte] throws IOException

30 for an input line]. You can also use the

public void abstract void write[int unsignedByte] throws IOException

31 methods to check for the availability of a desired input.

The commonly-used constructors are as follows. You can construct a

public void abstract void write[int unsignedByte] throws IOException

19 to parse a byte-based

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 [e.g.,

public void abstract void write[int unsignedByte] throws IOException

34], a disk file, or a given

File size is 417455 bytes
Elapsed Time is 61.834954 msec

For examples,

Example 1: The most common usage of

public void abstract void write[int unsignedByte] throws IOException

19 is to read primitive types and

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7 form the keyboard [

public void abstract void write[int unsignedByte] throws IOException

34], as follows:

The

public void abstract void write[int unsignedByte] throws IOException

20 methods throw

public void abstract void write[int unsignedByte] throws IOException

40 if the next token does not match the type to be parsed.

Example 2: You can easily modify the above program to read the inputs from a text file, instead of keyboard [

public void abstract void write[int unsignedByte] throws IOException

34].

Prepare the input file "

public void abstract void write[int unsignedByte] throws IOException

42" as follows:

public boolean accept[File dirName, String fileName]

0nextXxx[] and hasNextXxx[]

The

public void abstract void write[int unsignedByte] throws IOException

19 class implements

public void abstract void write[int unsignedByte] throws IOException

44 interface. You can use

public void abstract void write[int unsignedByte] throws IOException

45 coupled with

public void abstract void write[int unsignedByte] throws IOException

28 to iterate through all the

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7 tokens. You can also directly iterate through the primitive types via methods

public void abstract void write[int unsignedByte] throws IOException

31 and

public void abstract void write[int unsignedByte] throws IOException

20.

public void abstract void write[int unsignedByte] throws IOException

50 includes all primitive types [

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

17,

public void abstract void write[int unsignedByte] throws IOException

52,

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

13,

public abstract int read[] throws IOException

98,

public void abstract void write[int unsignedByte] throws IOException

55,

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

53 and

public void abstract void write[int unsignedByte] throws IOException

57],

public void abstract void write[int unsignedByte] throws IOException

58 and

public void abstract void write[int unsignedByte] throws IOException

59.

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

04 is not included but can be retrieved from

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7 via

public void abstract void write[int unsignedByte] throws IOException

62.

Delimiter

Instead of the default white spaces as the delimiter, you can set the delimiter to a chosen regular expression via these methods:

Example 3: Customized token delimiter

The regular expression

public void abstract void write[int unsignedByte] throws IOException

63 matches zero or more white spaces [

public void abstract void write[int unsignedByte] throws IOException

64] followed by "apple" followed by zero or more white spaces [

public void abstract void write[int unsignedByte] throws IOException

64]. An additional backslash [

File size is 417455 bytes
Elapsed Time is 2.938921 msec

8] is needed to use a backslash [

File size is 417455 bytes
Elapsed Time is 2.938921 msec

8] in Java

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7's literal. Read "Regular Expression" for more details.

Regexe Pattern Matching

You can use the following methods to find the next occurrence of the specified pattern using regular expressions:

Charset

By default,

public void abstract void write[int unsignedByte] throws IOException

19 uses the default charset to read the character from the input source. You can ask

public void abstract void write[int unsignedByte] throws IOException

19 to read text file which is encoded using a particular charset, by providing the charset name.

Example 4:

Formatted-Text Printing with printf[] method

JDK 1.5 introduces C-like

public void abstract void write[int unsignedByte] throws IOException

9 method [in classes

public void abstract void write[int unsignedByte] throws IOException

72 and

public void abstract void write[int unsignedByte] throws IOException

73] for formatted-text printing.

To write formatted-text to console [

public abstract int read[] throws IOException

04 or

public abstract int read[] throws IOException

05], you could simply use the convenience methods

public void abstract void write[int unsignedByte] throws IOException

76 or

public void abstract void write[int unsignedByte] throws IOException

77.

public void abstract void write[int unsignedByte] throws IOException

9 takes this syntax:

public boolean accept[File dirName, String fileName]

public void abstract void write[int unsignedByte] throws IOException

9 takes a variable number [zero or more] of arguments [or varargs]. Varargs was introduced in JDK 1.5 [that is the reason Java cannot support

public void abstract void write[int unsignedByte] throws IOException

9 earlier].

public void abstract void write[int unsignedByte] throws IOException

9 can be called from

public abstract int read[] throws IOException

04 or

public abstract int read[] throws IOException

05 [ which are

public boolean accept[File dirName, String fileName]

97s]. For example,

public boolean accept[File dirName, String fileName]

public boolean accept[File dirName, String fileName]

You can also use the

public void abstract void write[int unsignedByte] throws IOException

77 method, which is identical to

public void abstract void write[int unsignedByte] throws IOException

76.

Format Specifiers

A format specifier begins with

public void abstract void write[int unsignedByte] throws IOException

87 and ends with a conversion-type character [e.g.

public void abstract void write[int unsignedByte] throws IOException

88 for integer,

public void abstract void write[int unsignedByte] throws IOException

89 for

public void abstract void write[int unsignedByte] throws IOException

55 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

53], with optional parameters in between, as follows:

public boolean accept[File dirName, String fileName]

The optional argument_position specifies the position of the argument in the argument list. The first argument is
```
public void abstract void write[int unsignedByte] throws IOException
```
92, second argument is
```
public void abstract void write[int unsignedByte] throws IOException
```
93, and so on.
The optional width indicates the minimum number of characters to be output.
The optional precision restricts the number of characters [or number of decimal places for float-point numbers].

The mandatory conversion-type-character indicates how the argument should be formatted. For examples:

public void abstract void write[int unsignedByte] throws IOException

94,

public void abstract void write[int unsignedByte] throws IOException

95 [

public void abstract void write[int unsignedByte] throws IOException

57],

public void abstract void write[int unsignedByte] throws IOException

97,

public void abstract void write[int unsignedByte] throws IOException

98 [hex string],

public void abstract void write[int unsignedByte] throws IOException

99,

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

00 [string],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

01,

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

02 [character],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

03 [decimal integer],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

04 [octal integer],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

05,

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

06 [hexadecimal integer],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

07,

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

08 [float-point number in scientific notation],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

09 [floating-point number],

public void abstract void write[int unsignedByte] throws IOException

87 [percent sign]. The uppercase conversion code [e.g.,

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

00] formats the texts in uppercase.

Flag:

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

12 [left-justified],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

13 [include sign],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

14 [include leading space],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

15 [zero-padded],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

16 [include grouping separator].

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

17 [negative value in parentheses],

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

18 [alternative form].

Read JDK API

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

19's "" for details on format specifiers.

Examples

public boolean accept[File dirName, String fileName]

public boolean accept[File dirName, String fileName]

public boolean accept[File dirName, String fileName]

public boolean accept[File dirName, String fileName]

public boolean accept[File dirName, String fileName]

public abstract int read[] throws IOException

Formatted-Text Output via java.util.Formatter Class & format[] method

JDK 1.5 introduced

public void abstract void write[int unsignedByte] throws IOException

7 for formatted text input. It also introduced

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

19 for formatted text output.

public void abstract void write[int unsignedByte] throws IOException

8 is an interpreter for

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

23-style format strings. It supports layout justification and alignment, common formats for numeric, string, and date/time data, and locale-specific output, via the format specifiers.

The

public void abstract void write[int unsignedByte] throws IOException

8 has the following constructors:

public void abstract void write[int unsignedByte] throws IOException

8 supports

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

26/

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

27 [as

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

28] as output sink. It does not support

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7, probably because

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7 is immutable.

The

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

0 method can be used to write formatted text output:

public abstract int read[] throws IOException

Notice that the method

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

0 has the same syntax as the method

public void abstract void write[int unsignedByte] throws IOException

9, using the same set of format specifier as

public void abstract void write[int unsignedByte] throws IOException

Other methods are:

Example 1: Using a

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

27 [which implements

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

28] as the output sink for the

public void abstract void write[int unsignedByte] throws IOException

public abstract int read[] throws IOException

Read JDK API

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

19's "" for details on format specifiers.

Example 2: Setting the charset for

public void abstract void write[int unsignedByte] throws IOException

8's output.

String.format[]

The

public void abstract void write[int unsignedByte] throws IOException

8 with

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

27 as the output sink allows you to build up a formatted string progressively. To produce a simple formatted

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7, you can simply use the

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 method

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

44. This is handy in the

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

45 method, which is required to return a

File size is 417455 bytes
Elapsed Time is 61.834954 msec

7. For example,

public abstract int read[] throws IOException

File I/O in JDK 1.7

[This section was extracted from the Java Online Tutorial and JDK 7 API.]

JDK 1.7 greatly enhances supports for file I/O via new package

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

1 and its associated packages.

Interface java.nio.file.Path

A path string could be used to locate a file, a directory or a symbolic link. A symbolic link [or symlink] is a special file that references another file. A path string is system dependent, e.g., "

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

8" in Windows or "

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

9" in Unix. Windows uses back-slash

File size is 417455 bytes
Elapsed Time is 2.938921 msec

0 as the directory separator; while Unixes use forward-slash

File size is 417455 bytes
Elapsed Time is 2.938921 msec

1. Windows uses semi-colon

File size is 417455 bytes
Elapsed Time is 2.938921 msec

2 as path separator; while Unixes use colon

File size is 417455 bytes
Elapsed Time is 2.938921 msec

3. The "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

7" or "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

8" is called the root. Windows supports multiple roots, each maps to a drive [e.g., "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

7", "

File size is 417455 bytes
Elapsed Time is 61.834954 msec

0"]. Unix has single root ["

File size is 417455 bytes
Elapsed Time is 2.938921 msec

8"]. A path could be absolute [beginning from the root] or relative [which is relative to the current working directory]. Special notations "

File size is 417455 bytes
Elapsed Time is 61.834954 msec

2" and "

File size is 417455 bytes
Elapsed Time is 61.834954 msec

3" denote the current directory and the parent directory, respectively.

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

6 instance specifies the location of a file, or a directory, or a symbolic link.

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62 replaces

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

4 [of the standard I/O], which is less versatile and buggy.

Helper class java.nio.file.Paths

To create a

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62, use the

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 method

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

66 of the helper class

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

67. The helper class

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

68 contains exclusively

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 methods for creating

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62 objects.

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

71 returns a

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62 object by converting a given path string or

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

73.

For example,

As the directory-separator is system dependent, for writing portable and more flexible program, it is recommended to use an existing

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62 instance as an anchor to resolve the filename, e.g.,

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62 can be broken down as root, level-0, level-1, .... The method

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

76 returns the levels. The method

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

77 returns the name of level-i. For example,

Helper Class java.nio.file.Files

The class

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

78 contains exclusively

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 methods for file, directory and symlink operations such as create, delete, read, write, copy, move, etc.

Properties of a File/Directory

You can use

File size is 417455 bytes
Elapsed Time is 61.834954 msec

public void abstract void write[int unsignedByte] throws IOException

57 methods

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

82 and

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

83 to verify if a given

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62 exists or does not exist [as a file, directory or symlink]. A

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62 could be verified to exist, or not exist, or unknown [e.g., the program does not have access to the file]. If the status is unknown, the

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

86 and

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

87 returns

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

01.

You could also use

File size is 417455 bytes
Elapsed Time is 61.834954 msec

public void abstract void write[int unsignedByte] throws IOException

57 methods

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

91,

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

92 and

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

93 to verify whether a

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62 locates a file, directory, or symlink.

Many of these methods take an optional second argument of

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

95, which is applicable for symlink only. For example,

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

96 specifies do not follow the symlink.

For example, to get the size of a file in JDK 1.7:

Deleting a File/Directory

You can use

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 methods

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

98 to delete a file or directory. Directory can be deleted only if it is empty. A

public void abstract void write[int unsignedByte] throws IOException

57 method

File size is 417455 bytes
Elapsed Time is 2.938921 msec

00 is also available.

public abstract int read[] throws IOException

4Copying/Moving a File/Directory

You can use

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 methods

File size is 417455 bytes
Elapsed Time is 2.938921 msec

02 or

File size is 417455 bytes
Elapsed Time is 2.938921 msec

03 to copy or move a file or directory. The methods return the target

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

62.

The methods accepts an optional third argument of

File size is 417455 bytes
Elapsed Time is 2.938921 msec

05. For examples:

File size is 417455 bytes
Elapsed Time is 2.938921 msec

06 replaces the target if it exists;

File size is 417455 bytes
Elapsed Time is 2.938921 msec

07 copies the file attributes such as the dates;

File size is 417455 bytes
Elapsed Time is 2.938921 msec

08 specifies not to follow symlinks.

public abstract int read[] throws IOException

To copy a file into another directory:

public abstract int read[] throws IOException

6Reading/Writing Small Files

For small files, you can use

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 methods

File size is 417455 bytes
Elapsed Time is 2.938921 msec

10 [byte-based] and

File size is 417455 bytes
Elapsed Time is 2.938921 msec

11 [character-based] to read the entire file. You can use

File size is 417455 bytes
Elapsed Time is 2.938921 msec

12 [byte-based] or

File size is 417455 bytes
Elapsed Time is 2.938921 msec

13 [character-based] to write to a file.

The optional

File size is 417455 bytes
Elapsed Time is 2.938921 msec

14 includes:

File size is 417455 bytes
Elapsed Time is 2.938921 msec

15,

File size is 417455 bytes
Elapsed Time is 2.938921 msec

16,

File size is 417455 bytes
Elapsed Time is 2.938921 msec

17 [truncates the file to zero bytes],

File size is 417455 bytes
Elapsed Time is 2.938921 msec

18 [creates a new file and throws an exception if the file already exists],

File size is 417455 bytes
Elapsed Time is 2.938921 msec

19 [opens the file if it exists or creates a new file if it does not], among others.

Byte-based OperationCharacter-based Operation

Examples: The following example write a small text file [in "UTF-8"], and read the entire file back as bytes as well as characters.

Buffered Character-based I/O for Text Files

For Reading, use

File size is 417455 bytes
Elapsed Time is 2.938921 msec

20 method to open a text file, which returns a

public boolean accept[File dirName, String fileName]

47. Use

File size is 417455 bytes
Elapsed Time is 2.938921 msec

22 to read a line,

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

11 to read a char, or

File size is 417455 bytes
Elapsed Time is 2.938921 msec

24 to read into a char-array.

For Writing, use the

File size is 417455 bytes
Elapsed Time is 2.938921 msec

25 method to open a output text file, which returns a

public boolean accept[File dirName, String fileName]

48. Use

File size is 417455 bytes
Elapsed Time is 2.938921 msec

27 to write a character,

File size is 417455 bytes
Elapsed Time is 2.938921 msec

28 or

File size is 417455 bytes
Elapsed Time is 2.938921 msec

29 to write characters.

public abstract int read[] throws IOException

7Byte-Based Stream I/O

Use

File size is 417455 bytes
Elapsed Time is 2.938921 msec

30 to allocate an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 for reading raw bytes; and

File size is 417455 bytes
Elapsed Time is 2.938921 msec

32 to allocate an

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07 for writing. The

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

06 and

public String[] list[FilenameFilter filter]
public File[] listFiles[FilenameFilter filter]
public File[] listFiles[FileFilter filter]

07 returned are not buffered.

Example: Similar to the previous program which read/write the entire file, this program read/write via Buffered I/O.

Creating a New File/Directory/Symlink

Beside using the

File size is 417455 bytes
Elapsed Time is 2.938921 msec

36 method with

File size is 417455 bytes
Elapsed Time is 2.938921 msec

14 of

File size is 417455 bytes
Elapsed Time is 2.938921 msec

19 or

File size is 417455 bytes
Elapsed Time is 2.938921 msec

18, you can also use

File size is 417455 bytes
Elapsed Time is 2.938921 msec

40 method to create an empty file. You can use the default file attributes or optionally define the initial attributes of the file.

public abstract int read[] throws IOException

The

File size is 417455 bytes
Elapsed Time is 2.938921 msec

41 includes: [TODO]

DOS:
Unixes: Nine file permissions: read, write, and execute permissions for the file owner, members of the same group, and "everyone else", e.g., "
```
File size is 417455 bytes
Elapsed Time is 2.938921 msec
```
42".

Example: [TODO]

Similarly, you can create a new directory, symlink as follows:

Example:

Creating a Temporary File/Directory

Example: [TODO]

File Attributes

You can use one of the

File size is 417455 bytes
Elapsed Time is 2.938921 msec

43 methods to read all the basic attribute of a path.

FileChannel

Random Access File

The Interface

File size is 417455 bytes
Elapsed Time is 2.938921 msec

44 supports random access.

Directory Operations

List all root directoriesListing a directory

You can list the contents of a directory by using the

File size is 417455 bytes
Elapsed Time is 2.938921 msec

45 method. The returned

File size is 417455 bytes
Elapsed Time is 2.938921 msec

46 object implements

File size is 417455 bytes
Elapsed Time is 2.938921 msec

47. You can iterate thru the entries with for-each loop.

public abstract int read[] throws IOException

Example: List the contents of a directory

In addition, you can include a glob pattern to filter the entries.

public void abstract void write[int unsignedByte] throws IOException

Example: List the contents of a directory filtered by a glob.

Glob

A glob is a subset of regular expression.

File size is 417455 bytes
Elapsed Time is 2.938921 msec

48 matches zero or more character [0+].

File size is 417455 bytes
Elapsed Time is 2.938921 msec

49 matches any one character.

File size is 417455 bytes
Elapsed Time is 2.938921 msec

50 behaves like

File size is 417455 bytes
Elapsed Time is 2.938921 msec

48, but can cross directory boundary, for matching on full path.

File size is 417455 bytes
Elapsed Time is 2.938921 msec

52 encloses a set of sub-patterns separated by ','.

File size is 417455 bytes
Elapsed Time is 2.938921 msec

53 encloses a set of single character or a range of character with

File size is 417455 bytes
Elapsed Time is 3781.500581 msec

12, e.g., [aeiou], [a-z], [0-9].

Any other character matches itself. To match

File size is 417455 bytes
Elapsed Time is 2.938921 msec

48,

File size is 417455 bytes
Elapsed Time is 2.938921 msec

49 or special characters, prefix with

File size is 417455 bytes
Elapsed Time is 2.938921 msec

For example: "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

58" matches entry starts with "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

59" and ends with "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

60", "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

61", or "

File size is 417455 bytes
Elapsed Time is 2.938921 msec

62".

You can also write your own codes to filter the entries.

public void abstract void write[int unsignedByte] throws IOException

The interface

File size is 417455 bytes
Elapsed Time is 2.938921 msec

63 declares one

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

public void abstract void write[int unsignedByte] throws IOException

57 method

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

9, which will be call-back for each entry. Those entries that resulted in false

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

9 will be discarded.

public void abstract void write[int unsignedByte] throws IOException

Example: The following program uses an anonymous instance of an anonymous

File size is 417455 bytes
Elapsed Time is 2.938921 msec

63 sub-class to filter the

File size is 417455 bytes
Elapsed Time is 2.938921 msec

46. The call-back method

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

9 returns

File size is 417455 bytes
Elapsed Time is 2.938921 msec

71 for regular files, and discards the rest. Take note that this filtering criterion cannot be implemented in a glob-pattern.

Walking the File Tree - Files.walkFileTree[]

You can use

File size is 417455 bytes
Elapsed Time is 61.834954 msec

5 method

File size is 417455 bytes
Elapsed Time is 2.938921 msec

73 ro recursively walk thru all the files from a starting directory.

First of all, you need to create an object that implements interface

File size is 417455 bytes
Elapsed Time is 2.938921 msec

74, which declares these

DataOutputStream out = new DataOutputStream[
                          new BufferedOutputStream[
                             new FileOutputStream["out.dat"]]];

6 methods:

These methods return an

File size is 417455 bytes
Elapsed Time is 2.938921 msec

76 of

File size is 417455 bytes
Elapsed Time is 2.938921 msec

77, which could take values of

File size is 417455 bytes
Elapsed Time is 2.938921 msec

78,

File size is 417455 bytes
Elapsed Time is 2.938921 msec

79,

File size is 417455 bytes
Elapsed Time is 2.938921 msec

80,

File size is 417455 bytes
Elapsed Time is 2.938921 msec

81.

Instead of implementing

File size is 417455 bytes
Elapsed Time is 2.938921 msec

74 interface, you could also extend from superclass

File size is 417455 bytes
Elapsed Time is 2.938921 msec

83, and override the selected methods.

There are two versions of

File size is 417455 bytes
Elapsed Time is 2.938921 msec

84. The first version take a starting directory and a

File size is 417455 bytes
Elapsed Time is 2.938921 msec

74, and transverse through all the levels, without following the symlinks.

public void abstract void write[int unsignedByte] throws IOException

Example:

The second version takes 2 additional arguments: the

File size is 417455 bytes
Elapsed Time is 2.938921 msec

86 specifies whether to follow symlink [e.g.,

File size is 417455 bytes
Elapsed Time is 2.938921 msec

87 or

File size is 417455 bytes
Elapsed Time is 2.938921 msec

88]; the

File size is 417455 bytes
Elapsed Time is 2.938921 msec

89 specifies the levels to visit [set to

File size is 417455 bytes
Elapsed Time is 2.938921 msec

90 for all levels].

Which of the following classes should be used for reading from a text file?

You use the Scanner class to read text files and the PrintWriter class to write text files.

Which Java class is the preferred class to use for writing to a binary file?

The preferred stream classes for processing binary files are ObjectInputStream and ObjectOutputStream. Each has methods to read/write data one byte at a time and can automatically convert numbers and characters to bytes. First, here is an example how to write some simple data to a binary file using ObjectOutputStream.

File and Directory

Class File size is 417455 bytes Elapsed Time is 3781.500581 msec4 [Pre-JDK 7]

Class File size is 417455 bytes Elapsed Time is 3781.500581 msec6 [JDK 7]

Stream I/O in Standard I/O [java.io Package]

Byte-Based I/O & Byte Streams

Reading from an InputStream

Writing to an OutputStream

Opening & Closing I/O Streams

Flushing the OutputStream

Implementations of abstract InputStream/OutputStream

Layered [or Chained] I/O Streams

File I/O Byte-Streams - FileInputStream & FileOutputStream

Buffered I/O Byte-Streams - BufferedInputStream & BufferedOutputStream

Formatted Data-Streams: DataInputStream & DataOutputStream

Network I/O

Character-Based I/O & Character Streams

Abstract superclass Reader and Writer

File I/O Character-Streams - FileReader & FileWriter

Buffered I/O Character-Streams - BufferedReader & BufferedWriter

Character Set [or Charset] - Package java.nio.charset [JDK 1.4]

Text File I/O - InputStreamReader and OutputStreamWriter

java.io.PrintStream & java.io.PrintWriter

Object Serialization and Object Streams

ObjectInputStream & ObjectOutputStream

java.io.Serializable & Externalizable Interfaces

Random Access Files

Compressed I/O Streams

Formatted Text I/O - java.util.Scanner & java.util.Formatter [JDK 1.5]

Formatted-Text Input via java.util.Scanner

Formatted-Text Printing with printf[] method

Formatted-Text Output via java.util.Formatter Class & format[] method

String.format[]

File I/O in JDK 1.7

Interface java.nio.file.Path

Helper class java.nio.file.Paths

Helper Class java.nio.file.Files

File Attributes

FileChannel

Random Access File

Directory Operations

Walking the File Tree - Files.walkFileTree[]

Which of the following classes should be used for reading from a text file?

Which Java class is the preferred class to use for writing to a binary file?

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Class
File size is 417455 bytes Elapsed Time is 3781.500581 msec
4 [Pre-JDK 7]

Class
File size is 417455 bytes Elapsed Time is 3781.500581 msec
6 [JDK 7]