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Java Fundamental Classes Reference

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The java.io Package
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PushbackReader

Name

PushbackReader

Synopsis

Class Name:

java.io.PushbackReader

Superclass:

java.io.FilterReader

Immediate Subclasses:

None

Interfaces Implemented:

None

Availability:

New as of JDK 1.1

Description

The PushbackReader class represents a character stream that allows data to be pushed back into the stream. In other words, after data has been read from a PushbackReader, it can be pushed back into the stream so that it can be reread. This functionality is useful for implementing things like parsers that need to read data and then return it to the input stream. PushbackReader is the character-oriented equivalent of PushbackInputStream.

Class Summary

public class java.io.PushbackReader extends java.io.FilterReader {
  // Constructors
  public PushbackReader(Reader in);
  public PushbackReader(Reader in, int size);
  // Instance Methods
  public void close();
  public boolean markSupported();
  public int read();
  public int read(char[] cbuf, int off, int len);
  public boolean ready();
  public void unread(int c);
  public void unread(char[] cbuf);
  public void unread(char[] cbuf, int off, int len);
}

Constructors

PushbackReader

public PushbackReader(Reader in)

Parameters

in

The reader to wrap.

Description

This constructor creates a PushbackReader that reads from the given Reader, using a pushback buffer with the default size of one byte.

public PushbackReader(Reader in, int size)

Parameters

in

The reader to wrap.

size

The size of the pushback buffer.

Description

This constructor creates a PushbackReader that reads from the given Reader, using a pushback buffer of the given size.

Instance Methods

close

public void close() throws IOException

Throws

IOException

If any kind of I/O error occurs.

Overrides

FilterReader.close()

Description

This method closes the reader and releases the system resources that are associated with it.

markSupported

public boolean markSupported()

Returns

The boolean value false.

Overrides

FilterReader.markSupported()

Description

This method returns false to indicate that this class does not support mark() and reset().

read

public int read() throws IOException

Returns

The next character of data or -1 if the end of the stream is encountered.

Throws

IOException

If any kind of I/O error occurs.

Overrides

FilterReader.read()

Description

This method reads a character of data. If there is any data in the pushback buffer, the method returns the next character in the pushback buffer. Otherwise, it calls the read() method of the underlying stream. The method blocks until the character is read, the end of the stream is encountered, or an exception is thrown.

public int read(char[] cbuf, int off, int len) throws IOException

Parameters

cbuf

An array of characters to be filled from the stream.

off

An offset into the array.

len

The number of characters to read.

Returns

The actual number of characters read or -1 if the end of the stream is encountered immediately.

Throws

IOException

If any kind of I/O error occurs.

Overrides

FilterReader.read(char[], int, int)

Description

This method copies characters from the stream into the given array cbuf, starting at index off and continuing for len characters. If the array can be populated solely from the pushback buffer, the method returns immediately. Otherwise, the read(char[], int, int) method of the underlying stream is called to make up the difference. The method blocks until some data is available.

ready

public boolean ready() throws IOException

Returns

A boolean value that indicates whether the stream is ready to be read.

Throws

IOException

If the stream is closed.

Overrides

FilterReader.ready()

Description

If there is data in the pushback buffer, or if the underlying stream is ready, this method returns true. The underlying stream is ready if the next read() is guaranteed not to block.

unread

public void unread(int c) throws IOException

Parameters

c

The value to push back.

Throws

IOException

If the pushback buffer is full.

Description

This method puts the given character into the pushback buffer.

public void unread(char[] cbuf) throws IOException

Parameters

cbuf

An array of characters to push back.

Throws

IOException

If the pushback buffer is full.

Description

This method puts all of the characters in the given array into the pushback buffer.

public void unread(char[] cbuf, int off, int len) throws IOException

Parameters

cbuf

An array of characters to push back.

off

An offset into the array.

len

The number of characters to push back.

Throws

IOException

If the pushback buffer is full.

Description

This method puts len characters from the given array, starting at offset off, into the pushback buffer.

Inherited Methods

Method

Inherited From

Method

Inherited From

clone()

Object

equals(Object)

Object

finalize()

Object

getClass()

Object

hashCode()

Object

mark(int)

FilterReader

notify()

Object

notifyAll()

Object

read(char[])

FilterReader

reset()

FilterReader

skip(long)

FilterReader

toString()

Object

wait()

Object

wait(long)

Object

wait(long, int)

Object

   

See Also

FilterReader, IOException, Reader


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