Updating Old Class Files

In some cases, the new Java Runtime Environment associated with this Java Plug-in release will not run class files that were generated with old compilers. The usual symptom is a java.lang.ClassFormatError that the virtual machine throws when it attempts to load such a class file. This failure has nothing specifically to do with the changes in this release. Rather, old bytecode compilers did not strictly adhere to proper class-file format in all situations when generating class files. Recent virtual machines are implemented to be strict in enforcing proper class file format, and this can lead to errors when they attempt to load old, improperly formatted class files. Some typical problems in some older class files are (this list is not exhaustive):

• There are extra bytes at the end of the class file;

• The class file contains method or field names that do not begin with a letter;

• The class attempts to access private members of another class;

• The class file has other format errors, including illegal constant pool indices and illegal UTF-8 strings;

• Some early (third-party) bytecode obfuscators produced class files that violated proper class-file format.

You can avoid this type of problem by recompiling your classes with the Javac bytecode compiler from the current Java 2 SDK. If you choose to use a third-party obfuscator, be sure to use one that produces class files that respect proper class-file format.