HashSet （需要重寫hashCode和equals方法）__基礎知識

一般描述的事物需要往集合中添加，那麼都需要重寫這兩個方法

刪除和判斷元素是否存在，都是先判斷hashCode 看看是否存在，若存在則繼續equals（）；

import java.util.*;class Person{private String name;private int age;Person(String name,int age){this.name=name;this.age=age;}public int hashCode()//重寫  {return name.hashCode()+age ;}public boolean equals(Object obj)//重寫   Object不能換{          if(!(obj instanceof Person))  return false;  Person p=(Person)obj;  System.out.println(this.name+"...."+p.name);  return this.name.equals(p.name)&&this.age==p.age;}public String getName(){return name;}public int getAge(){return age;}}class HashSetDemo {public static void main(String[] args) {HashSet hs=new HashSet();hs.add(new Person("lisi01",30));hs.add(new Person("lisi02",33));hs.add(new Person("lisi03",35));hs.add(new Person("lisi02",33));hs.add(new Person("lisi01",30));hs.add(new Person("lisi04",32));hs.add(new Person("lisi03",35));Iterator it=hs.iterator();while(it.hasNext()){           Person p=(Person)it.next();;   sop(p.getName()+" "+p.getAge());}}public static void sop(Object obj)    {          System.out.println(obj);}}