Step through JDK source code in IntelliJ IDEA

Solution 1:

If you look in [File menu ->] Settings -> Debugger -> Stepping you will see a list "Do not step into these classes", probably with "java.*" listed there. Is that the case? You can turn that off there.

Apparently the debug information is not available. According to this thread:

Sadly the JDK classes have debug information for parameters and local variable stripped off.

Years ago I filed a request that Idea should deduce the necessary information from the source code (basically converting variable names to indexes into the methods local var):
Debugger: Show variable information when no debug info

Please vote/comment.

As a workaround you can re-compile the JDK from sources, but you need to exclude some classes which do not have all needed source code attached.

Interestingly, you can download the beta version of Java 6u18, which has debug information in it (in the DEBUG bundle).

Solution 2:

UPDATE: IntelliJ IDEA 13+ version can provide local variables information without debug info.

Java classes which are part of the JDK are compiled without debug info for the size and performance reasons. If you want debug info in these classes, you'll either need to install a development version of the JDK where the classes are built with the debug info or rebuild the parts of JDK you want to debug from source with the debug info enabled and configure the new JDK with these versions of classes in jars.

This thread provides the instructions how to rebuild JDK classes in rt.jar from the source code with debugging information.

P.S. This question is not specific to IntelliJ IDEA.