nio-Buffer

Buffer属性

capacity: buffer的容量 

A buffer's capacity is the number of elements it contains.  The capacity of a buffer is never negative and never changes. limit: 写时limit=capacity，读时limit=buffer内数据的长度

A buffer's limit is the index of the first element that should not be read or written.  A buffer's limit is never negative and is never greater than its capacity.   position:下一个读写的位置

A buffer's position is the index of the next element to be read or written.  A buffer's position is never negative and is never greater than its limit.  

Buffer方法

flip:

把limit设为当前position，把position设为0，一般在从Buffer读出数据前调用。

public final Buffer flip() {    limit = position;    position = 0;    mark = -1;    return this;}
clear:
把position设为0，把limit设为capacity，一般在把数据写入Buffer前调用。
public final Buffer clear() {    position = 0;    limit = capacity;    mark = -1;    return this;}
rewind：
把position设为0，limit不变，一般在把数据重写入Buffer前调用。
public final Buffer rewind() {    position = 0;    mark = -1;    return this;}