Two most useful Eclipse plugings

1)      FindBugs is a defect detection tool for Java that uses static analysis to look for more than 200 bug patterns, such as null pointer de-references, infinite recursive loops, bad uses of the Java libraries and deadlocks. FindBugs can identify hundreds of serious defects in large applications (typically about 1 defect per 1000-2000 lines of non-commenting source statements). FindBugs is open source (LGPL), has been downloaded more than 500,000 times and is used by many major companies and financial institutions.

2)      UCDetector (Unnecessary Code Detector) is a eclipse Plug In tool to find unnecessary (dead) public java code.
For example public classes, methods or fields which have no references.

The problems found by UCDetector, are only suggestions. Before changing code, you should really know what you are doing! If UCDetector tells you, that there are no references your code still may be used by:

Reflection 

Frameworks like Spring, Hibernate or Eclipse which declare dependencies in property files, xml files (extension-points) ...

Third party code, which is using your API

Jars in your work-space

It's good idea to do a full text search in work-space for the piece of code, you want to change.