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pushbackinputstream.java
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1995-08-11
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/*
* @(#)PushbackInputStream.java 1.6 95/01/31 Jonathan Payne
*
* Copyright (c) 1994 Sun Microsystems, Inc. All Rights Reserved.
*
* Permission to use, copy, modify, and distribute this software
* and its documentation for NON-COMMERCIAL purposes and without
* fee is hereby granted provided that this copyright notice
* appears in all copies. Please refer to the file "copyright.html"
* for further important copyright and licensing information.
*
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
* THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
* TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
* PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
* ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
* DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
*/
package java.io;
/**
* An input stream that has a 1 byte push back buffer.
* It also keeps track of line numbers.
* @version 1.6, 31 Jan 1995
* @author Jonathan Payne
*/
public
class PushbackInputStream extends FilterInputStream {
/**
* Push back character.
*/
protected int pushBack = -1;
/**
* The current line number.
*/
protected int lineNumber = 1;
/**
* Creates a PushbackInputStream.
* @param in the input stream
*/
public PushbackInputStream(InputStream in) {
super(in);
}
/**
* Reads a byte. Will block if no input is available.
* @return the byte read, or -1 if the end of the
* stream is reached.
* @exception IOException i/o error occurred
*/
public int read() {
int c;
if ((c = pushBack) != -1) {
pushBack = -1;
} else {
c = super.read();
}
if (c == '\n') {
lineNumber += 1;
}
return c;
}
/**
* Reads into an array of bytes.
* Blocks until some input is available.
* This method should be overridden in a subclass for
* efficiency (the default implementation reads 1 byte
* at a time).
* @param b the buffer into which the data is read
* @param off the start offset of the data
* @param len the maximum number of bytes read
* @return the actual number of bytes read, -1 is
* returned when the end of the stream is reached.
* @exception IOException i/o error occurred
*/
public int read(byte bytes[], int offset, int length) {
int c = read();
if (c == -1) {
bytes[offset] = (byte)c;
return 1;
}
return -1;
}
/**
* Pushes back a character.
* @param ch the character to push back.
* @exception Exception Attempt to push back more than one character.
*/
public void unread(int ch) {
if (pushBack != -1) {
throw new Exception("Attempt to unread more than one character!");
}
pushBack = ch;
}
/**
* Returns the current line number.
*/
public int currentLine() {
return lineNumber;
}
}