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

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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