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简介

Set集合不包含重复的元素，相同的元素只保存一个，不包含相等的两个元素，Set至多只能包含一个NULL元素。Set的实现类都是基于Map来实现的，其中HashSet是通过HashMap来实现的，TreeSet是通过TreeMap实现的。

类图

遍历方式

public static void main(String[] args) {
        Set
   
     set = new HashSet<>();    set.add("Lions are the most mighty of all animals in Africa.");    set.add("Those kids always have so much enthusiasm about studying.");    set.add("Calligraphy is the art of beautiful handwriting.");    // 迭代器    Iterator
    
      iterator = set.iterator();    while (iterator.hasNext()) {
            System.out.println(iterator.next());    }    System.out.println("-------------------------------------------");    // 迭代器for循环    for (iterator = set.iterator();iterator.hasNext();){
            System.out.println(iterator.next());    }    System.out.println("-------------------------------------------");    // 加强型for循环    for (String str : set) {
            System.out.println(str);    }}
    
   

源码

参照JDK1.8版本

Query Operations

//返回集合的大小int size();//集合为空，返回true，否则，返回falseboolean isEmpty();//判断集合是否包含指定对象oboolean contains(Object o);//返回set集合的迭代器Iterator
   
     iterator();//Returns an array containing all of the elements in this set.Object[] toArray();//Returns an array containing all of the elements in this set;
    
      T[] toArray(T[] a);
    
   

Modification Operations

//添加一个元素boolean add(E e);//删除一个元素boolean remove(Object o);

Bulk Operations

//Returns true if this set contains all of the elements of the //specified collection. boolean containsAll(Collection
    c);//将指定集合的全部元素添加到当前集合中boolean addAll(Collection
    c);/*** In other words, removes from this set all of its elements * that are not contained in the specified collection.  **/boolean retainAll(Collection
    c);/*** Removes from this set all of its elements that are contained* in the specified collection (optional operation).  */boolean removeAll(Collection
    c);/*** Removes all of the elements from this set (optional operation).*/void clear();

Comparison and hashing

//判断是否相等boolean equals(Object o);//Returns the hash code value for this set. int hashCode();