outputstream类是所有的字符输出类的父类，他是一个抽象类。
对于OutputStream类来说，其最基础的方法就是：write().
public abstract void write(int b) throws IOException
这个方法，写一个无符号字符（在0-255之间）
举例如下：
import java.io.*; public class AsciiChart { public static void main(String[] args) { for (int i = 32; i < 127; i++) { System.out.write(i); // break line after every eight characters. if (i % 8 == 7) System.out.write(' '); else System.out.write(' '); } System.out.write(' '); } }
在这里，请注意输出： 和 。分别对应数字是：10和9，也可以这么写：
import java.io.*; public class AsciiChart { public static void main(String[] args) { for (int i = 32; i < 127; i++) { System.out.write(i); // break line after every eight characters. if (i % 8 == 7) System.out.write(10); else System.out.write(9); } System.out.write(' '); } }
输出如下：
% java AsciiChart
! " # $ % & '
( ) * + , - . /
0 1 2 3 4 5 6 7
8 9 : ; < = > ?
@ A B C D E F G
H I J K L M N O
P Q R S T U V W
X Y Z [ ] ^ _
` a b c d e f g
h i j k l m n o
p q r s t u v w
x y z { | } ~
而outputstream的这个抽象类具体定义如下：
/*
* Copyright (c) 1994, 2004, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*
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*
*
*
*
*
*
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*
*/
package java.io;
/**
* This abstract class is the superclass of all classes representing
* an output stream of bytes. An output stream accepts output bytes
* and sends them to some sink.
* <p>
* Applications that need to define a subclass of
* <code>OutputStream</code> must always provide at least a method
* that writes one byte of output.
*
* @author Arthur van Hoff
* @see java.io.BufferedOutputStream
* @see java.io.ByteArrayOutputStream
* @see java.io.DataOutputStream
* @see java.io.FilterOutputStream
* @see java.io.InputStream
* @see java.io.OutputStream#write(int)
* @since JDK1.0
*/
public abstract class OutputStream implements Closeable, Flushable {
/**
* Writes the specified byte to this output stream. The general
* contract for <code>write</code> is that one byte is written
* to the output stream. The byte to be written is the eight
* low-order bits of the argument <code>b</code>. The 24
* high-order bits of <code>b</code> are ignored.
* <p>
* Subclasses of <code>OutputStream</code> must provide an
* implementation for this method.
*
* @param b the <code>byte</code>.
* @exception IOException if an I/O error occurs. In particular,
* an <code>IOException</code> may be thrown if the
* output stream has been closed.
*/
public abstract void write(int b) throws IOException;
/**
* Writes <code>b.length</code> bytes from the specified byte array
* to this output stream. The general contract for <code>write(b)</code>
* is that it should have exactly the same effect as the call
* <code>write(b, 0, b.length)</code>.
*
* @param b the data.
* @exception IOException if an I/O error occurs.
* @see java.io.OutputStream#write(byte[], int, int)
*/
public void write(byte b[]) throws IOException {
write(b, 0, b.length);
}
/**
* Writes <code>len</code> bytes from the specified byte array
* starting at offset <code>off</code> to this output stream.
* The general contract for <code>write(b, off, len)</code> is that
* some of the bytes in the array <code>b</code> are written to the
* output stream in order; element <code>b[off]</code> is the first
* byte written and <code>b[off+len-1]</code> is the last byte written
* by this operation.
* <p>
* The <code>write</code> method of <code>OutputStream</code> calls
* the write method of one argument on each of the bytes to be
* written out. Subclasses are encouraged to override this method and
* provide a more efficient implementation.
* <p>
* If <code>b</code> is <code>null</code>, a
* <code>NullPointerException</code> is thrown.
* <p>
* If <code>off</code> is negative, or <code>len</code> is negative, or
* <code>off+len</code> is greater than the length of the array
* <code>b</code>, then an <tt>IndexOutOfBoundsException</tt> is thrown.
*
* @param b the data.
* @param off the start offset in the data.
* @param len the number of bytes to write.
* @exception IOException if an I/O error occurs. In particular,
* an <code>IOException</code> is thrown if the output
* stream is closed.
*/
public void write(byte b[], int off, int len) throws IOException {
if (b == null) {
throw new NullPointerException();
} else if ((off < 0) || (off > b.length) || (len < 0) ||
((off + len) > b.length) || ((off + len) < 0)) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return;
}
for (int i = 0 ; i < len ; i++) {
write(b[off + i]);
}
}
/**
* Flushes this output stream and forces any buffered output bytes
* to be written out. The general contract of <code>flush</code> is
* that calling it is an indication that, if any bytes previously
* written have been buffered by the implementation of the output
* stream, such bytes should immediately be written to their
* intended destination.
* <p>
* If the intended destination of this stream is an abstraction provided by
* the underlying operating system, for example a file, then flushing the
* stream guarantees only that bytes previously written to the stream are
* passed to the operating system for writing; it does not guarantee that
* they are actually written to a physical device such as a disk drive.
* <p>
* The <code>flush</code> method of <code>OutputStream</code> does nothing.
*
* @exception IOException if an I/O error occurs.
*/
public void flush() throws IOException {
}
/**
* Closes this output stream and releases any system resources
* associated with this stream. The general contract of <code>close</code>
* is that it closes the output stream. A closed stream cannot perform
* output operations and cannot be reopened.
* <p>
* The <code>close</code> method of <code>OutputStream</code> does nothing.
*
* @exception IOException if an I/O error occurs.
*/
public void close() throws IOException {
}
}