closing the streams of I/o

问题:

What are the bad things that can happen when I don't close the stream?

Does the close operation automatically flush?

Are all the streams closed after the program exits?

Thanks in advance.

回答1:

Bad things that can happen when you don't close your streams:

• you can run out of file handles
• data that you think is written to disk may still be in the buffer (only)
• files might still be locked for other processes (depends on the platform)
• ...

Yes, close operation always flushes the stream.

All file handles that the OS is aware of are closed. This means effectively that FileOutputStream, FileInputStream and the input/output of a Socket will be closed. But if you wrap a FileOutputStream in a BufferedOutputStream then that BufferedOutputStream will not be known to the OS and won't be closed/flushed on shutdown. So data written to the BufferedOutputStream but not yet flushed to the FileOutputStream can be lost.

回答2:

1) You tie up system resources unnecessarily (e.g. file descriptors). Possibly to the extent of running out of them.

2) Yes (although you should check the documentation of the particular stream you're interested in to be sure).

3) Yes

回答3:

To qualify, when you perform a close(), it flushes the data and closes the file handle. If you exit, the file handle is closed but un-flushed data is lost.