FindBugs is an open source program created by Bill Pugh and David Hovemeyer which looks for bugs in Java code.It uses static analysis to identify hundreds of different potential types of errors in Java programs.FindBugs operates on Java bytecode,rather than source code.The software is distributed as a stand-alone GUI application. There are also plug-ins available for Eclipse,Netbeans,IntelliJ IDEA,and Hudson.

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http://findbugs.sourceforge.net/index.html