Question:
Why do I have problems running some programs with Java 2?

Answer:
Many Java class libraries and programs written before Java 2 use a technique called obfuscation to make it difficult for their source code to be reverse-engineered. Obfuscation often resulted in class files that did not comply with the Java class file binary specification. They worked with Java 1.1 because most JVMs did not implement completely correct class file verification. With Java 2, the situation has changed, and Sun’s JVM implements very strict class file verification. If you have a program that uses incompatible classfiles, you should see a ClassFormatError exception. If you are unable to recompile the code, you can make the classes work with Java 2 byeither using the oldjava command provided with JDK 1.2 or using the -noverify option when running java.