A file hash is a string of numbers and letters that are unique to a specific file, like a thumbprint.
There are many different algorithms for generating hashes. The most common are MD5 and SHA-1. Each different algorithm generates a completely different hash if given the same data.
These hashes can be used to prove that a certain file has not been tampered with in any way. File hashes are commonly used to verify large file downloads. For example, if you download the most recent Ubuntu distribution, you can verify that you received the file without a single bit being altered by hashing the file and comparing it to the file hash that Ubuntu posts on their site.
This file hasher program comes with support for several hashing algorithms including MD2, MD5, SHA-1, SHA-256, SHA-384, and SHA-512.
JChecksum is released under the GPL. The source code is included in the JAR file. Download the plain JAR file to access the source code.
I have also made JChecksum avaliable on SourceForge. You can find it at: http://jchecksum.sourceforge.net/
Version: 3.0
Last Updated: Mar 2, 2009
Release Date: Jan 10, 2009
Download: JChecksum