Question

The write() function in java appends new data to end of file. Here is my question; how the java knows end of file?

1. By reading whole file to find end of file
2. It knows where the end of file

Which one? Thanks in advance

Answer 1

For Unix / Linux at least, the answer is that the operating system takes care of this. Java just makes use of the operating system provided file descriptor that keeps track of the application’s current position within the file.

• If you opened the file normally (append == false), then a write writes data at the file descriptor’s current position, and then updates it to point to the position immediately after the data just written.

• If you opened the file in append mode (append == true), then each write writes data at the current end of file.

Note that other Unix / Linux I/O operations use and update the current position of a file descriptor; e.g. read, seek and tell.

Here is my question; how the java knows end of file?

1. By reading whole file to find end of file: No

2. It knows where the end of file: Not exactly. It is typically the operating system that knows, not
   Java.