Today I have discovered very nice feature of Eclipse Debugger - it is possible to get rid of the
"Source not found" message while debugging. One obvious solution is to add the source to the code that we want to debug, but there are times when we don't have access to the sources of some libraries. In this situation we can use
Step Filtering preference:

Now, when we invoke
Step Into on a code which is included in this preference it will be treated as
Step Over - we won't see the
"Source not found" message any more.