How can I tell why/how two class files are different?

Question

I am trying to recreate some old source. I have two classes, one from my new source and one from the lost source. The both classes will decompile to identical source. However, a bit level compare of the classes still shows differences. How do tell what causes these differences?

GC_

Answer 1

I found just using javap to be very helpful.

I ran this command for both classes:

javap -version -l -v -p -c -s -sysinfo ClassName.class > temp.txt

Then I compared the two files. This uncovered the difference I was looking for. It was a line number thing. I found eclipse's decompiler helpful, too.