package java.util; import org.checkerframework.checker.lock.qual.*; public abstract class AbstractQueue<E extends Object> extends AbstractCollection<E> implements Queue<E> { protected AbstractQueue() {} public boolean add(E a1) { throw new RuntimeException("skeleton method"); } public E remove() { throw new RuntimeException("skeleton method"); } public E element() { throw new RuntimeException("skeleton method"); } public void clear() { throw new RuntimeException("skeleton method"); } public boolean addAll(Collection<? extends E> a1) { throw new RuntimeException("skeleton method"); } // public abstract boolean isEmpty(@GuardSatisfied AbstractQueue<E> this); }