What if you were able to discover potential problems in your code prior to building it? Interestingly enough, there are Eclipse plugins for tools such as JDepend and CheckStyle that can help you discover problems before they are manifested in software. In
Simian (Similarity Analyser) identifies duplication in Java, C#, C, C++, COBOL, Ruby, JSP, ASP, HTML, XML, Visual Basic source code and even plain text files. In fact, simian can be used on any human readable files such as ini files, deployment descriptor
Cobertura is a free Java tool that calculates the percentage of code accessed by tests. It can be used to identify which parts of your Java program are lacking test coverage. It is based on jcoverage.