Software's complexity and accelerated development schedules makes avoiding defects difficult.

"Finding and fixing a software problem after delivery is often 100 times more expensive than finding and fixing it during the requirements and design phase." - Barry Boehm, Victor R. Basili

Identifying potential bugs during development and fixing could save time and money. Testing tools provide a means to identify functional bugs and basically ensure 'fitness of use'. However simple mistakes made by developers could elude into production environment and cause major show stoppers and such mistakes are seldom caught by testing tools.

Given the complexity of software a mistype conditional construct or a wrong API call is enough to stop the show. Moreover testing needs testcases and creating exhaustive testcases is time consuming and costlier. To overcome the limitation of testing tools and reduce testing effort, we need a specialized analysis of source code to find such mistakes before the source is released for testing or production environment.

Swat4j automatically finds potential bugs in Java source code by analyzing  for common bug patterns and reports the location of such potential bugs. Since the process is automatic and integrated with Eclipse IDE developers find it easy to run this analysis and fix potential bugs before they release their module for integration or testing.

The major advantage of Swat4j analysis is that it does not need testcases.

See documentation. Reference->Rules->Potential Bugs for a complete list of patterns analyzed by Swat4j.

Reference & further reading
Software Defect Reduction Top 10 List - Barry Boehm and Victor R. Basili