Snippet from the JDK8 Collection interface demonstrating the addition of a default stream() method.

Collection.java

public interface Collection<E> extends Iterable<E> {
  
  // Traditional, abstract methods:

  int size();
  boolean contains(Object o);
  boolean add(E e);
  boolean remove(Object o);
  // Etc...

  // New methods stream() and parallelStream() with default implementations:

  default Stream<E> stream() {
    return Streams.stream(() -> Streams.spliterator(iterator(), size(), Spliterator.SIZED), Spliterator.SIZED);
  }

  default Stream<E> parallelStream() {
    return stream().parallel();
  }

}