How do I “decompile” Java class files?

Question

What program can I use to decompile a class file? Will, I get Java code, or is it just JVM assembly code?

On Java performance questions on this site, I often see responses from people who have "decompile" the Java class file to see how the compiler optimizes certain things.

Answer 1

Most of the Java decompilers downloadable now from Internet such as “DJ Java Decompiler” or “Cavaj Java Decompiler” are powered by JAD. However, these compilers can't display Java 5 sources.

Java Decompiler (Yet another Fast Java decompiler) has:

  Explicit assistance for decompiling and analyzing Java 5+ “.class” files.

    A refined GUI:

To download this compiler click here.

Or, you can also decompile online, check here.