Because Java(TM) programs are interrupted, Java class files contain sufficient information to rebuild source code, unless precautions are taken. If you are worried about decompiling, don't release class files (servlets), compile your programs to executables for specific platforms, don't include debug information in your class files (javac -O Source.java) and/or obfuscate your code with a good bytecode obfuscator/name mangler/class file shrinker. Some decompilers will still be able to reconstruct source code from obfuscated classes. However, the regenerated source will be less than mangled up considerably with new method/variable names and constructs. For a list of available resources to help, see http://java.about.com/msubsecurity.htm.