Set继承了Collection接口

方法

size

返回set中包含的元素个数，如果包含的元素多于Integer.MAX_VALUE，则返回Integer.MAX_VALUE;

    int size();

contains

如果set中包含指定的元素，返回true。这分为两种情况，指定元素为null，set中也包含null或者指定元素为o，set中存在e使得o.equals(e)

/*
     * @throws ClassCastException if the type of the specified element
     *         is incompatible with this set
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this
     *         set does not permit null elements
     */
    boolean contains(Object o);

add

向set中添加元素，如果set中已经存在该元素，那么这次调用后set不变并返回false

/**
     * @throws UnsupportedOperationException if the <tt>add</tt> operation
     *         is not supported by this set
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this set
     * @throws NullPointerException if the specified element is null and this
     *         set does not permit null elements
     * @throws IllegalArgumentException if some property of the specified element
     *         prevents it from being added to this set
     */
    boolean add(E e);

remove

从set中移除特定元素(o= =null ?e==null:o.equals(e))

/**
     * @throws ClassCastException if the type of the specified element
     *         is incompatible with this set
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws NullPointerException if the specified element is null and this
     *         set does not permit null elements
     * (<a href="Collection.html#optional-restrictions">optional</a>)
     * @throws UnsupportedOperationException if the <tt>remove</tt> operation
     *         is not supported by this set
     */
    boolean remove(Object o);