无参数的read()方法是每次读取一个char字符，有参数的read(buffer, 0, buffer.length)是将读取的内容先放到buffer中去，而返回的是每次读取的char字符个数！
1、
c = isr.read() Reads a single character 读取单个character
the next byte of data, or -1 if the end of the file is reached
返回下一个next byte of data
2、
c = isr.read(byte[] , start,len) Reads characters into a portion of an array 读取多个charachters
返回the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.
返回total所有的number，也就数量
The character read, or -1 if the end of the stream has been reached
如果流读取结束，将返回-1
The number of characters read, or -1 if the end of the stream has been reached
如果流读取结束，返回-1
所以read()不是表示读取的计数，或者位置,表示下一个byte.
随时随地看视频
