Eclipse Hot Swap Debugging

Maybe this is a well known feature, but it was news to me. The Eclipse debugger supports swapping code out at runtime when debugging (JVM 1.4 and later). Ensure Build Automatically is enabled, then run your application in debug mode. When stopped at a breakpoint, change the code you want to change and save the file. The code will be automatically swapped into your application without restarting - pretty cool.

This article http://www.ibm.com/developerworks/library/os-ecbug/ gives some more details regarding debugging with Eclipse.