public abstract interface Frobnicate { public void twiddle(String s); } Which is a correct class?

• public abstract class Frob implements Frobnicate { public abstract void twiddle(String s) { } }
• public abstract class Frob implements Frobnicate { }
• public class Frob extends Frobnicate { public void twiddle(Integer i) { } }
• public class Frob implements Frobnicate { public void twiddle(Integer i) { } }