Operations on files

To execute reading and writing operations on a file, we must open the file before doing the operations, and close it after we are finished operating on it.

• Opening a file means to indicate to the operating system that we want to operate on a file from within a Java program, and the operating system verifies whether such operations are possible and allowed. There are two ways of opening a file: opening for reading and opening for writing, which cause a different behavior of the operating system. For example, two files may be opened at the same time by two applications for reading, but not for writing; or a file on a CD may be opened for reading, but not for writing. In many programming languages (including Java), opening a file for writing means actually to create a new file.
• Closing a file means to indicate to the operating system that the file that was previously opened is not being used anymore by the program. Closing a file also has the effect of ensuring that the data written on the file are effectively transferred to the hard-disk.