Class java.io.PushbackInputStream - JDK 5 Documentation v1.1.8, Java 2 SDK 英文文档

All Packages  Class Hierarchy  This Package  Previous  Next  Index

Class java.io.PushbackInputStream

java.lang.Object
   |
   +----java.io.InputStream
           |
           +----java.io.FilterInputStream
                   |
                   +----java.io.PushbackInputStream

public class PushbackInputStream
extends FilterInputStream

This class is an input stream filter that provides a buffer into which data can be "unread." An application may unread data at any time by pushing it back into the buffer, as long as the buffer has sufficient room. Subsequent reads will read all of the pushed-back data in the buffer before reading from the underlying input stream.

This functionality is useful when a fragment of code should read an indefinite number of data bytes that are delimited by particular byte values. After reading the terminating byte the code fragment can push it back, so that the next read operation on the input stream will re-read that byte.

buf: The pushback buffer.
pos: The position within the pushback buffer from which the next byte will be read.

PushbackInputStream(InputStream): Creates a new pushback input stream with a one-byte pushback buffer.
PushbackInputStream(InputStream, int): Creates a new pushback input stream with a pushback buffer of the specified size.

available(): Returns the number of bytes that can be read from this input stream without blocking.
markSupported(): Tests if this input stream supports the mark and reset methods, which it does not.
read(): Reads the next byte of data from this input stream.
read(byte[], int, int): Reads up to len bytes of data from this input stream into an array of bytes.
unread(byte[]): Pushes back an array of bytes by copying it to the front of the pushback buffer.
unread(byte[], int, int): Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer.
unread(int): Pushes back a byte by copying it to the front of the pushback buffer.

buf

 protected byte buf[]

The pushback buffer.

pos

 protected int pos

The position within the pushback buffer from which the next byte will be read. When the buffer is empty, pos is equal to buf.length; when the buffer is full, pos is equal to zero.

PushbackInputStream

 public PushbackInputStream(InputStream in,
                            int size)

Creates a new pushback input stream with a pushback buffer of the specified size.

Parameters:: in - the input stream from which bytes will be read.; size - the size of the pushback buffer.

PushbackInputStream

 public PushbackInputStream(InputStream in)

Creates a new pushback input stream with a one-byte pushback buffer.

Parameters:: in - the input stream from which bytes will be read.

read

 public int read() throws IOException

Reads the next byte of data from this input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

This method returns the most recently pushed-back byte, if there is one, and otherwise calls the read method of its underlying input stream and returns whatever value that method returns.

Returns:: the next byte of data, or -1 if the end of the stream has been reached.
Throws: IOException: if an I/O error occurs.
Overrides:: read in class FilterInputStream
See Also:: read

read

 public int read(byte b[],
                 int off,
                 int len) throws IOException

Reads up to len bytes of data from this input stream into an array of bytes. This method first reads any pushed-back bytes; after that, if fewer than than len bytes have been read then it reads from the underlying input stream. This method blocks until at least 1 byte of input is available.

Parameters:: b - the buffer into which the data is read.; off - the start offset of the data.; len - the maximum number of bytes read.
Returns:: the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.
Throws: IOException: if an I/O error occurs.
Overrides:: read in class FilterInputStream

unread

 public void unread(int b) throws IOException

Pushes back a byte by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value (byte)b.

Parameters:: b - the int value whose low-order byte is to be pushed back.
Throws: IOException: If there is not enough room in the pushback buffer for the byte.

unread

 public void unread(byte b[],
                    int off,
                    int len) throws IOException

Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value b[off], the byte after that will have the value b[off+1], and so forth.

Parameters:: b - the byte array to push back.; off - the start offset of the data.; len - the number of bytes to push back.
Throws: IOException: If there is not enough room in the pushback buffer for the specified number of bytes.

unread

 public void unread(byte b[]) throws IOException

Pushes back an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value b[0], the byte after that will have the value b[1], and so forth.

Parameters:: b - the byte array to push back
Throws: IOException: If there is not enough room in the pushback buffer for the specified number of bytes.

available

 public int available() throws IOException

Returns the number of bytes that can be read from this input stream without blocking. This method calls the available method of the underlying input stream; it returns that value plus the number of bytes that have been pushed back.

Returns:: the number of bytes that can be read from the input stream without blocking.
Throws: IOException: if an I/O error occurs.
Overrides:: available in class FilterInputStream
See Also:: in

markSupported

 public boolean markSupported()

Tests if this input stream supports the mark and reset methods, which it does not.

Returns:: false, since this class does not support the mark and reset methods.
Overrides:: markSupported in class FilterInputStream
See Also:: mark, reset

All Packages  Class Hierarchy  This Package  Previous  Next  Index

Submit a bug or feature - Version 1.1.8 of Java Platform API Specification
Java is a trademark or registered trademark of Sun Microsystems, Inc. in the US and other countries.
Copyright 1995-1999 Sun Microsystems, Inc. 901 San Antonio Road,
Palo Alto, California, 94303, U.S.A. All Rights Reserved.