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Reader.javaAPI DocJava SE 5 API8199Fri Aug 26 14:57:00 BST 2005java.io

Reader

public abstract class Reader extends Object implements Closeable, Readable
Abstract class for reading character streams. The only methods that a subclass must implement are read(char[], int, int) and close(). Most subclasses, however, will override some of the methods defined here in order to provide higher efficiency, additional functionality, or both.
see
BufferedReader
see
LineNumberReader
see
CharArrayReader
see
InputStreamReader
see
FileReader
see
FilterReader
see
PushbackReader
see
PipedReader
see
StringReader
see
Writer
version
1.27, 03/12/19
author
Mark Reinhold
since
JDK1.1

Fields Summary
protected Object
lock
The object used to synchronize operations on this stream. For efficiency, a character-stream object may use an object other than itself to protect critical sections. A subclass should therefore use the object in this field rather than this or a synchronized method.
private static final int
maxSkipBufferSize
Maximum skip-buffer size
private char[]
skipBuffer
Skip buffer, null until allocated
Constructors Summary
protected Reader()
Create a new character-stream reader whose critical sections will synchronize on the reader itself.

	this.lock = this;
    
protected Reader(Object lock)
Create a new character-stream reader whose critical sections will synchronize on the given object.

param
lock The Object to synchronize on.

	if (lock == null) {
	    throw new NullPointerException();
	}
	this.lock = lock;
    
Methods Summary
public abstract voidclose()
Close the stream. Once a stream has been closed, further read(), ready(), mark(), or reset() invocations will throw an IOException. Closing a previously-closed stream, however, has no effect.

exception
IOException If an I/O error occurs

public voidmark(int readAheadLimit)
Mark the present position in the stream. Subsequent calls to reset() will attempt to reposition the stream to this point. Not all character-input streams support the mark() operation.

param
readAheadLimit Limit on the number of characters that may be read while still preserving the mark. After reading this many characters, attempting to reset the stream may fail.
exception
IOException If the stream does not support mark(), or if some other I/O error occurs

	throw new IOException("mark() not supported");
    
public booleanmarkSupported()
Tell whether this stream supports the mark() operation. The default implementation always returns false. Subclasses should override this method.

return
true if and only if this stream supports the mark operation.

	return false;
    
public intread(java.nio.CharBuffer target)
Attempts to read characters into the specified character buffer. The buffer is used as a repository of characters as-is: the only changes made are the results of a put operation. No flipping or rewinding of the buffer is performed.

param
target the buffer to read characters into
return
The number of characters added to the buffer, or -1 if this source of characters is at its end
throws
IOException if an I/O error occurs
throws
NullPointerException if target is null
throws
ReadOnlyBufferException if target is a read only buffer

        int len = target.remaining();
        char[] cbuf = new char[len];
        int n = read(cbuf, 0, len);
        if (n > 0)
            target.put(cbuf, 0, n);
        return n;
    
public intread()
Read a single character. This method will block until a character is available, an I/O error occurs, or the end of the stream is reached.

Subclasses that intend to support efficient single-character input should override this method.

return
The character read, as an integer in the range 0 to 65535 (0x00-0xffff), or -1 if the end of the stream has been reached
exception
IOException If an I/O error occurs

	char cb[] = new char[1];
	if (read(cb, 0, 1) == -1)
	    return -1;
	else
	    return cb[0];
    
public intread(char[] cbuf)
Read characters into an array. This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.

param
cbuf Destination buffer
return
The number of characters read, or -1 if the end of the stream has been reached
exception
IOException If an I/O error occurs

	return read(cbuf, 0, cbuf.length);
    
public abstract intread(char[] cbuf, int off, int len)
Read characters into a portion of an array. This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.

param
cbuf Destination buffer
param
off Offset at which to start storing characters
param
len Maximum number of characters to read
return
The number of characters read, or -1 if the end of the stream has been reached
exception
IOException If an I/O error occurs

public booleanready()
Tell whether this stream is ready to be read.

return
True if the next read() is guaranteed not to block for input, false otherwise. Note that returning false does not guarantee that the next read will block.
exception
IOException If an I/O error occurs

	return false;
    
public voidreset()
Reset the stream. If the stream has been marked, then attempt to reposition it at the mark. If the stream has not been marked, then attempt to reset it in some way appropriate to the particular stream, for example by repositioning it to its starting point. Not all character-input streams support the reset() operation, and some support reset() without supporting mark().

exception
IOException If the stream has not been marked, or if the mark has been invalidated, or if the stream does not support reset(), or if some other I/O error occurs

	throw new IOException("reset() not supported");
    
public longskip(long n)
Skip characters. This method will block until some characters are available, an I/O error occurs, or the end of the stream is reached.

param
n The number of characters to skip
return
The number of characters actually skipped
exception
IllegalArgumentException If n is negative.
exception
IOException If an I/O error occurs


                                                                      
          
	if (n < 0L) 
	    throw new IllegalArgumentException("skip value is negative");
	int nn = (int) Math.min(n, maxSkipBufferSize);
	synchronized (lock) {
	    if ((skipBuffer == null) || (skipBuffer.length < nn))
		skipBuffer = new char[nn];
	    long r = n;
	    while (r > 0) {
		int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
		if (nc == -1)
		    break;
		r -= nc;
	    }
	    return n - r;
	}