Java InputStream read返回int

问题

InputStream 操作的是字节流，read字面上理解应该返回字节，为什么api中返回的是int

public abstract int read()
                  throws IOException
Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.
A subclass must provide an implementation of this method.

Returns:
the next byte of data, or -1 if the end of the stream is reached.
Throws:
IOException - if an I/O error occurs.

原因

• byte表示的范围是-128～127，不能表示0～255
• EOF（-1）？
• 为什么不用short的原因是int效率更高（字节对齐？），虽然内存占用会大一些

参考

SOF