Set接口

package java.util;
//无重复元素集合，继承Collection接口，所有方法意义基本同父接口
public interface Set<E> extends Collection<E> {
    // Query Operations
    int size();
    boolean isEmpty();
    boolean contains(Object o);
    Iterator<E> iterator();
    Object[] toArray();
    <T> T[] toArray(T[] a);
    // Modification Operations
    boolean add(E e);
    boolean remove(Object o);
    // Bulk Operations
    boolean containsAll(Collection<?> c);
    boolean addAll(Collection<? extends E> c);
    boolean retainAll(Collection<?> c);//求交集 this交c
    boolean removeAll(Collection<?> c);//求差集 this减c
    void clear();
    // Comparison and hashing
    boolean equals(Object o);
    int hashCode();
    @Override
    default Spliterator<E> spliterator() {
        return Spliterators.spliterator(this, Spliterator.DISTINCT);
    }
}