Eclipse java debugging: source not found

Eclipse debugging works with the class actually loaded by the program.

The symptoms you describe sounds like the class in question was not found in the project, but in a distribution jar without debug info found before the project you are working with.

This can happen for several reasons but have a look at the location where the classes showing this behaviour is found (look in the navigation pane to identify it). You will most likely need to change the build path of the project to avoid using this jar and have the JVM use the project instead.

EDIT: Note that as of 2018 it is common to use a build framework like Maven, where the build path is managed by the m2e plugin so this problem should be very less frequent than when the question was asked. If you use Maven and m2e, make sure to enable Preferences / Maven / "Download Artifact Sources" or right-click the project, Maven / "Download Sources".

Just 3 steps to configuration Eclipse IDE:

Note: After updating the Source Lookup paths, you'll have to stop and restart your debug session. Otherwise, the file with the missing source will continue to show "missing source".

Edit Source Lookup Select the Edit Source Lookup... command [ Edit Source Lookup ] to open the Source Path Dialog, which allows you to make changes to the source lookup path of the selected debug target.

IMPORTANT Restart Eclipse after this last step.