When default methods were introduced in Java 8, some developers thought they would be the same as abstract classes. That’s not true, however, because interfaces can’t have state.

Using an anonymous class to pass functionality as a method argument (Comparer.java) public abstract class Comparer { public abstract int compare(int x, int y); } ...

Sealed classes make Java an even more powerful and expressive language and set the stage for even more sophisticated techniques such as pattern matching, which we'll explore in a subsequent article. A ...