How do I get BlueJ to use Java 5 on MacOS X?
With modern MacOS X versions, Java 5 (or 6) is the default. When Java 5 was initially released for MacOS X, it was not the default and BlueJ would continue to use Java 1.4. The instructions to change this are here. Not found? If the answer to your question was not in the list, please read How to ask for help.