For what purpose they are using flush() in Java?

Question

In Java, flush() method is using in streams. But I dont understand what are all the purpose of using this method?

fin.flush();

tell me some suggestions.

Answer 1

From the docs:

The flush method flushes the output stream and forces any buffered output bytes to be written out. The general contract of flush is that calling it is an indication that, if any bytes previously written have been buffered by the implementation of the output stream, such bytes should immediately be written to their intended destination.

The buffering is mainly done to improve the I/O performance. More on this can be read from this article: Tuning Java I/O Performance

Answer 2

Streams are often accessed by threads that periodically empty their content and, for example, display it on the screen, send it to a socket or write it to a file. This is done for performance reasons. Flushing an output stream means that you want to stop, wait for the content of the stream to be completely transferred to its destination, and then resume execution with the stream empty and the content sent.