Comparing Two Files

[Bharadwaj Adepu]

How do i compare two files using Java.
What classes and Packages caon i use?

[Campbell Ritchie]

Don't understand the problem. Do you mean comparing the sizes, contents or what? Have you been through the methods in the File class? Would you have to read the entire contents into a String and compare the two String?

[Bharadwaj Adepu]

I mean comparing the contents of the two files i.e. i want to know whether the two files are identical.

[Campbell Ritchie]

If they are text files, try:
Use a Scanner to iterate through the files.
Whenever you get a new line append it to a StringBuilder.
When myScanner.hasNext() shows false you can stop.

The StringBuilders won't show equal, but you can get them into a String and test like this:

return builder1.toString().equals(builder2.toString());

That's one way to do it.

[Jim Yingst]

I would first check if the lengths are equal, and if not, return false. Then open two FileInputStreams wrapped with BufferedInputStreams, one for each file. Then write a loop that reads one byte from each file, and returns false if the bytes are not equal. Keep looping until one the end of a file is reached. (You already know they're the same length at this point, so you should reach the end of both files simultaneously.) If you reach the end successfully without returning false, then you can return true instead - all the bytes must be equal.

Note that this technique works equally well regardless of whether you're using text files or binary files. It just tests whether they are exactly equal, or not.