22.13

java.io.PushbackInputStream

THE PACKAGE JAVA.IO

22.13 The Class

java.io.PushbackInputStream

A

PushbackInputStream

 adds functionality to another input stream, namely the

ability to  push back  or  unread  one byte. This is useful in situations where it is

convenient for a fragment of code to read an indefinite number of data bytes that

are delimited by a particular byte value; after reading the terminating byte, the

code fragment can  unread  it, so that the next read operation on the input stream

will reread the byte that was pushed back. For example, bytes representing the

characters constituting an identifier might be terminated by a byte representing an

operator character; a method whose job is to read just an identifier can read until it

sees the operator and then push the operator back to be re read.

public class PushbackInputStream extends FilterInputStream {

protected int pushBack =  1;

public PushbackInputStream(InputStream in);

public int read() throws IOException;

public int read(byte[] bytes, int offset, int length)

throws IOException, NullPointerException,

IndexOutOfBoundsException;

public void unread(int ch) throws IOException;

public int available() throws IOException;

public boolean markSupported();

}

22.13.1

protected int pushBack =  1;

If this field has a nonnegative value, it is a byte that was pushed back. If this field

is

 1

, there is currently no pushed back byte.

22.13.2

public PushbackInputStream(InputStream in)

This constructor initializes a newly created

PushbackInputStream

 by saving its

argument, the input stream

in

, for later use. Initially, there is no pushed back byte

(the field

pushBack

 is initialized to

 1

).

22.13.3

public int read() throws IOException

See the general contract of the

read

 method of

InputStream

 ( 22.3.1).

If

pushBack

 is not

 1

, the value of

pushBack

 is returned and

pushBack

 is set

to

 1

. Otherwise, a byte is obtained from the contained input stream.

Overrides the

read

 method of

FilterInputStream

 ( 22.9.3).

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