When compiling this code:

public class Test {
     public void start() {
         if (false) {
             new Runnable() {
                 @Override
                 public void run() {}
             };
         }
     }

     private static class SomeClass {}

     private static class SomeOtherClass extends SomeClass {}
}

javac generates a class name Test$1 that can't be verified. Any attempt to load that class will provoke a ClassFormatError