Example:

    public class Test
    {
        class Foo implements Runnable
    }

Applying "implement all abstract methods" on Foo results in:

    public class Test
    {
        class Foo implements Runnable

            public void run()
            {
                throw new UnsupportedOperationException("Not supported yet.");
            }
        class Foo implements Runnable
    }

I.e. "class Foo implements Runnable" is duplicated.