package java.util;
import org.checkerframework.dataflow.qual.Pure;
import org.checkerframework.checker.nullness.qual.Nullable;
// Subclasses of this interface/class may opt to prohibit null elements
public abstract class AbstractSet<E extends @Nullable Object> extends AbstractCollection<E> implements Set<E> {
protected AbstractSet() {}
@Pure public boolean equals(@Nullable Object a1) { throw new RuntimeException("skeleton method"); }
@Pure public int hashCode() { throw new RuntimeException("skeleton method"); }
public boolean removeAll(Collection<?> a1) { throw new RuntimeException("skeleton method"); }
}