关于缓冲器ByteBuffer的三个方法：flip(),clear(),remind()。
一、flip():反转此缓冲区，将限制设置为当前位置，然后将位置设置为 0 ！

之前的写操作会不断更新当前位置，当写操作完成之后，需调用此方法，将限制位置设置为当前位置，将当前位置设置为0，这样下一个读操作会从0开始，直到限制位置。

Java代码  

1. /** 
2.   * Flips this buffer.  The limit is set to the current position and then 
3.   * the position is set to zero.  If the mark is defined then it is 
4.   * discarded. 
5.   * 
6.   * <p> This method is often used in conjunction with the {@link 
7.   * java.nio.ByteBuffer#compact compact} method when transferring data from 
8.   * one place to another.  </p> 
9.   * 
10.   * @return  This buffer 
11.   */  
12.  public final Buffer flip() {  
13.      limit = position;  
14.      position = 0;  
15.      mark = -1;  
16.      return this;  
17.  }  
   /**
     * Flips this buffer.  The limit is set to the current position and then
     * the position is set to zero.  If the mark is defined then it is
     * discarded.
     *
     * <p> This method is often used in conjunction with the {@link
     * java.nio.ByteBuffer#compact compact} method when transferring data from
     * one place to another.  </p>
     *
     * @return  This buffer
     */
    public final Buffer flip() {
        limit = position;
        position = 0;
        mark = -1;
        return this;
    }
 
 Java代码  
1. public byte get() {  
2.     return hb[ix(nextGetIndex())];  
3. }  
4.   
5. final int nextGetIndex() {  // package-private  
6.     if (position >= limit)  
7.         throw new BufferUnderflowException();  
8.     return position++;  
9. }  
    public byte get() {
        return hb[ix(nextGetIndex())];
    }
 
    final int nextGetIndex() { // package-private
        if (position >= limit)
            throw new BufferUnderflowException();
        return position++;
    }

二、remain():与flip不同的是，不会修改限制位置。

比如初始化时：

Java代码  

1. ByteBuffer buffer=ByteBuffer.allocate(1024);  

ByteBuffer buffer=ByteBuffer.allocate(1024);

那么做读操作的时候就会读到第(1024-1)个索引，而flip却不一定能读到(1024-1)个索引，这取决于他的写操作的数据长度。

Java代码  

1. /** 
2.  * Rewinds this buffer.  The position is set to zero and the mark is 
3.  * discarded. 
4.  * 
5.  * <p> Invoke this method before a sequence of channel-write or <i>get</i> 
6.  * operations, assuming that the limit has already been set 
7.  * appropriately.  For example: 
8.  * 
9.  * <blockquote><pre> 
10.  * out.write(buf);    // Write remaining data 
11.  * buf.rewind();      // Rewind buffer 
12.  * buf.get(array);    // Copy data into array</pre></blockquote> 
13.  * 
14.  * @return  This buffer 
15.  */  
16. public final Buffer rewind() {  
17.     position = 0;  
18.     mark = -1;  
19.     return this;  
20. }  
    /**
     * Rewinds this buffer.  The position is set to zero and the mark is
     * discarded.
     *
     * <p> Invoke this method before a sequence of channel-write or <i>get</i>
     * operations, assuming that the limit has already been set
     * appropriately.  For example:
     *
     * <blockquote><pre>
     * out.write(buf);    // Write remaining data
     * buf.rewind();      // Rewind buffer
     * buf.get(array);    // Copy data into array</pre></blockquote>
     *
     * @return  This buffer
     */
    public final Buffer rewind() {
        position = 0;
        mark = -1;
        return this;
    }

三、clear():“清除”此缓冲区，将位置设置为 0，将限制设置为容量！此方法不能实际清除缓冲区中的数据，但从名称来看它似乎能够这样做，这样命名是因为它多数情况下确实是在清除数据时使用。因为调用该方法后，我们一般都会调用FileChannel.read(buff)或者buff.put()来把新的数据放到buff中，此时原来的内容就会被新的内容所覆盖！也不是全部覆盖，而是覆盖掉新数据所包含的字节数！所以看起来好象就是原来的内容被删除一样！

Java代码  

1. /** 
2.  * Clears this buffer.  The position is set to zero, the limit is set to 
3.  * the capacity, and the mark is discarded. 
4.  * 
5.  * <p> Invoke this method before using a sequence of channel-read or 
6.  * <i>put</i> operations to fill this buffer.  For example: 
7.  * 
8.  * <blockquote><pre> 
9.  * buf.clear();     // Prepare buffer for reading 
10.  * in.read(buf);    // Read data</pre></blockquote> 
11.  * 
12.  * <p> This method does not actually erase the data in the buffer, but it 
13.  * is named as if it did because it will most often be used in situations 
14.  * in which that might as well be the case. </p> 
15.  * 
16.  * @return  This buffer 
17.  */  
18. public final Buffer clear() {  
19.     position = 0;  
20.     limit = capacity;  
21.     mark = -1;  
22.     return this;  
23. }  
    /**
     * Clears this buffer.  The position is set to zero, the limit is set to
     * the capacity, and the mark is discarded.
     *
     * <p> Invoke this method before using a sequence of channel-read or
     * <i>put</i> operations to fill this buffer.  For example:
     *
     * <blockquote><pre>
     * buf.clear();     // Prepare buffer for reading
     * in.read(buf);    // Read data</pre></blockquote>
     *
     * <p> This method does not actually erase the data in the buffer, but it
     * is named as if it did because it will most often be used in situations
     * in which that might as well be the case. </p>
     *
     * @return  This buffer
     */
    public final Buffer clear() {
        position = 0;
        limit = capacity;
        mark = -1;
        return th


四、ByteBuffer类中提供position(),remaining(),hasRemaining()，limit()等方法来验证以上三点。

五、上述代码中提到的:

Java代码  

1. and the mark is discarded.