Java学习日记-集合SetTest02

关于往Set集合中存储的元素，该元素的hashCode和equals方法.

HashMap中有一个put方法，put(key,value) key是无序不可重复的.

结论：存储在HashSet集合或者HashMap集合key部分的元素，需要同时重写hashCode+equals

import java.util.*;
public class SetTest02 {

	public static void main(String[] args){
		
		//创建集合
		Set es = new HashSet();
		
		Employee e1 = new Employee("jack","1000");
		Employee e2 = new Employee("jack","1000");
		Employee e3 = new Employee("Smith","1000");
		Employee e4 = new Employee("Cook","2001");
		Employee e5 = new Employee("Mark","3001");
		Employee e6 = new Employee("Timi","3000");
		
		System.out.println(e1.hashCode());
		System.out.println(e2.hashCode());
		
		
		//添加元素
		es.add(e1);
		es.add(e2);
		es.add(e3);
		es.add(e4);
		es.add(e5);
		es.add(e6);
		
		//查看集合个数
		System.out.println(es.size());
		
		
	}
	
}
//根据现实业务逻辑得知
class Employee{
	
	String name;//姓名
	
	String no;//编号
	
	//constuctor
	Employee(String name,String no){
		this.name = name;
		this.no = no;
	}
	//重写equals方法
	//如果员工编号相同，并且名字也相同，则是同一个对象
	public boolean equals(Object o){
		if(this==o){
			return true;
		}
		if(o instanceof Employee){
			Employee e = (Employee)o;
			if(e.no.equals(this.no)&&e.name.equals(this.name)){
				return true;
			}
		}
		return false;
	}
	//重写hashCode方法
	public int hashCode(){
		//以员工编号分组
		return no.hashCode();
	}
}