How can I open Java .class files in a human-readable way?
jd-gui is the best decompiler at the moment. it can handle newer features in Java, as compared to the getting-dusty JAD.
As pointed out by @MichaelMyers, use
javap -c <name of java class file>
to get the JVM assembly code. You may also redirect the output to a text file for better visibility.
javap -c <name of java class file> > decompiled.txt
If you don't mind reading bytecode, javap should work fine. It's part of the standard JDK installation.
Usage: javap <options> <classes>... where options include: -c Disassemble the code -classpath <pathlist> Specify where to find user class files -extdirs <dirs> Override location of installed extensions -help Print this usage message -J<flag> Pass <flag> directly to the runtime system -l Print line number and local variable tables -public Show only public classes and members -protected Show protected/public classes and members -package Show package/protected/public classes and members (default) -private Show all classes and members -s Print internal type signatures -bootclasspath <pathlist> Override location of class files loaded by the bootstrap class loader -verbose Print stack size, number of locals and args for methods If verifying, print reasons for failure