What is the purpose of Manifest file
<p><a href="http://java.sun.com/developer/Books/javaprogramming/JAR/basics/manifest.html" rel="nofollow">http://java.sun.com/developer/Books/javaprogramming/JAR/basics/manifest.html</a></p>

<p>What does a manifest file do?
What is the purpose of it?</p>

<pre><code>Manifest-Version: 1.0

Name: java/math/BigDecimal.class
SHA1-Digest: TD1GZt8G11dXY2p4olSZPc5Rj64=
MD5-Digest: z6z8xPj2AW/Q9AkRSPF0cg==

Name: java/math/BigInteger.class
SHA1-Digest: oBmrvIkBnSxdNZzPh5iLyF0S+bE=
MD5-Digest: wFymhDKjNreNZ4AzDWWg1Q==
</code></pre>

<p>Does it update these classes in the jar automatically if there any changes in the server?</p>
