Debugging a Java Application could be fun and using debugging to explore JDK classes is even more fun. This helps in exploring the internals of JDK as well as broadens ones perspective of how things work. Unfortunately, stepping into JDK classes during debugging is disabled by default. Let’s see how to enable stepping into JDK classes in IntelliJ Idea.
Updating debug settings to enable stepping into JDK classes
Open IntelliJ Preferences, as shown in picture below
Click on Build,Execution and Deployment -> Debugger -> Stepping. You shall see a dialogue box as shown below
Under the section “Do not step into the classes” on right side, uncheck the classes you want to debug i.e. com.sun.* and java.* Click Apply and you are set. Here is how the final settings would look like