On Java performance questions on this site I often see responses from people who have "decompiled" the Java class file to see how the compiler optimizes certain things.
What program can I use to decompile a class file? Does you actually get Java code, or is it just JVM assembly code?
Thanks!
To see Java source code check some decompiler. Go search for jad.
If you want to see bytecodes, just use javap which comes with the JDK.
There's a few decompilers out there... a quick search yields:
and many more.
These produce Java code. Java comes with something that lets you see JVM byte code (javap).
There's a few programs you can use. You will get the actual Java code. Sometimes the code will have been obfuscated so method are called one letter or number or a random mix of letters and numbers.
I use JAD Decompiler.
There is a eclipse plugin to it. pretty nice: jadeclipse
Most decompilers for Java are based on JAD. It's a great tool, but unfortunately hasn't been updated for a while and does not handle Java 1.5+ classes very well. I have not seen any tools that will properly handle 1.5+ classes.
Soot is an option for newer Java code. At least it has the advantage of still being recently maintained...
Also, Java Decompiler is a decompiler with both a stand-alone GUI and Eclipse integration.
Lastly, Jdec hasn't been mentioned, though it's not as polished as other options.