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InputStream.java
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1998-09-22
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/*
* @(#)InputStream.java 1.22 98/07/01
*
* Copyright 1995-1998 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information"). You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/
package java.io;
/**
* This abstract class is the superclass of all classes representing
* an input stream of bytes.
* <p>
* Applications that need to define a subclass of
* <code>InputStream</code> must always provide a method that returns
* the next byte of input.
*
* @author Arthur van Hoff
* @version 1.22, 07/01/98
* @see java.io.BufferedInputStream
* @see java.io.ByteArrayInputStream
* @see java.io.DataInputStream
* @see java.io.FilterInputStream
* @see java.io.InputStream#read()
* @see java.io.OutputStream
* @see java.io.PushbackInputStream
* @since JDK1.0
*/
public abstract class InputStream {
/**
* Reads the next byte of data from this input stream. The value
* byte is returned as an <code>int</code> in the range
* <code>0</code> to <code>255</code>. If no byte is available
* because the end of the stream has been reached, the value
* <code>-1</code> is returned. This method blocks until input data
* is available, the end of the stream is detected, or an exception
* is thrown.
* <p>
* A subclass must provide an implementation of this method.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* stream is reached.
* @exception IOException if an I/O error occurs.
* @since JDK1.0
*/
public abstract int read() throws IOException;
/**
* Reads up to <code>b.length</code> bytes of data from this input
* stream into an array of bytes.
* <p>
* The <code>read</code> method of <code>InputStream</code> calls
* the <code>read</code> method of three arguments with the arguments
* <code>b</code>, <code>0</code>, and <code>b.length</code>.
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> is there is no more data because the end of
* the stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.InputStream#read(byte[], int, int)
* @since JDK1.0
*/
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
/**
* Reads up to <code>len</code> bytes of data from this input stream
* into an array of bytes. This method blocks until some input is
* available. If the argument <code>b</code> is <code>null</code>, a
* <code>NullPointerException</code> is thrown.
* <p>
* The <code>read</code> method of <code>InputStream</code> reads a
* single byte at a time using the read method of zero arguments to
* fill in the array. Subclasses are encouraged to provide a more
* efficient implementation of this method.
*
* @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 total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.InputStream#read()
* @since JDK1.0
*/
public int read(byte b[], int off, int len) throws IOException {
if (len <= 0) {
return 0;
}
int c = read();
if (c == -1) {
return -1;
}
b[off] = (byte)c;
int i = 1;
try {
for (; i < len ; i++) {
c = read();
if (c == -1) {
break;
}
if (b != null) {
b[off + i] = (byte)c;
}
}
} catch (IOException ee) {
}
return i;
}
/**
* Skips over and discards <code>n</code> bytes of data from this
* input stream. The <code>skip</code> method may, for a variety of
* reasons, end up skipping over some smaller number of bytes,
* possibly <code>0</code>. The actual number of bytes skipped is
* returned.
* <p>
* The <code>skip</code> method of <code>InputStream</code> creates
* a byte array of length <code>n</code> and then reads into it until
* <code>n</code> bytes have been read or the end of the stream has
* been reached. Subclasses are encouraged to provide a more
* efficient implementation of this method.
*
* @param n the number of bytes to be skipped.
* @return the actual number of bytes skipped.
* @exception IOException if an I/O error occurs.
* @since JDK1.0
*/
public long skip(long n) throws IOException {
/* ensure that the number is a positive int */
byte data[] = new byte[(int) (n & 0xEFFFFFFF)];
return read(data);
}
/**
* Returns the number of bytes that can be read from this input
* stream without blocking. The available method of
* <code>InputStream</code> returns <code>0</code>. This method
* <B>should</B> be overridden by subclasses.
*
* @return the number of bytes that can be read from this input stream
* without blocking.
* @exception IOException if an I/O error occurs.
* @since JDK1.0
*/
public int available() throws IOException {
return 0;
}
/**
* Closes this input stream and releases any system resources
* associated with the stream.
* <p>
* The <code>close</code> method of <code>InputStream</code> does nothing.
*
* @exception IOException if an I/O error occurs.
* @since JDK1.0
*/
public void close() throws IOException {}
/**
* Marks the current position in this input stream. A subsequent
* call to the <code>reset</code> method repositions this stream at
* the last marked position so that subsequent reads re-read the same
* bytes.
* <p>
* The <code>readlimit</code> arguments tells this input stream to
* allow that many bytes to be read before the mark position gets
* invalidated.
* <p>
* The <code>mark</code> method of <code>InputStream</code> does nothing.
*
* @param readlimit the maximum limit of bytes that can be read before
* the mark position becomes invalid.
* @see java.io.InputStream#reset()
* @since JDK1.0
*/
public synchronized void mark(int readlimit) {}
/**
* Repositions this stream to the position at the time the
* <code>mark</code> method was last called on this input stream.
* <p>
* The <code>reset</code> method of <code>InputStream</code> throws
* an <code>IOException</code>, because input streams, by default, do
* not support <code>mark</code> and <code>reset</code>.
* <p>
* Stream marks are intended to be used in
* situations where you need to read ahead a little to see what's in
* the stream. Often this is most easily done by invoking some
* general parser. If the stream is of the type handled by the
* parser, it just chugs along happily. If the stream is not of
* that type, the parser should toss an exception when it fails,
* which, if it happens within readlimit bytes, allows the outer
* code to reset the stream and try another parser.
*
* @exception IOException if this stream has not been marked or if the
* mark has been invalidated.
* @see java.io.InputStream#mark(int)
* @see java.io.IOException
* @since JDK1.0
*/
public synchronized void reset() throws IOException {
throw new IOException("mark/reset not supported");
}
/**
* Tests if this input stream supports the <code>mark</code>
* and <code>reset</code> methods. The <code>markSupported</code>
* method of <code>InputStream</code> returns <code>false</code>.
*
* @return <code>true</code> if this true type supports the mark and reset
* method; <code>false</code> otherwise.
* @see java.io.InputStream#mark(int)
* @see java.io.InputStream#reset()
* @since JDK1.0
*/
public boolean markSupported() {
return false;
}
}