package test;

import org.junit.Test;

import po.Person;

import java.util.HashMap;

import java.util.IdentityHashMap;

import java.util.Map;

/**

 * Created by Administrator on 2015/9/16.

 */

public class TestMap {

    /**

     * map插入相同key问题，value会不会覆盖

     */

    @Test

    public void testMap(){

        //HashMap中key的内容相同，则覆盖

        Map<String,Object> map1 = new HashMap<>();

        map1.put("张三",1);

        map1.put("张三",2);

        map1.put(new String("张三"),3);  //根据String特性，这三条内容相同，前两条地址相同

        map1.put("李四", 4);

        for (String s : map1.keySet()) {

            System.out.println(s+"======"+map1.get(s));

        }

        /** 结果

         *   张三======3

             李四======4

         */

        System.out.println("=====================================");

        //IdentityHashMap中key的内存地址必须完全相同才会覆盖

        Map<String,Object> map2 = new IdentityHashMap<>();

        map2.put("张三",1);

        map2.put("张三",2);

        map2.put(new String("张三"),3);//

        map2.put("李四", 4);

        for (String s : map2.keySet()) {

            System.out.println(s+"===="+map2.get(s));

        }

        /**

         * 李四====4

         张三====2

         张三====3

         */

        System.out.println("=====================================");

        Map<Person,Object> map3 = new IdentityHashMap<>();

        map3.put(new Person("张三", 11), 1);

        map3.put(new Person("张三", 11), 3);

        map3.put(new Person("李四", 11), 4);

        for (Person s : map3.keySet()) {

            System.out.println(s.toString()+"===="+map3.get(s));

        }

        /**

         * po.Person@165474cf====1

         po.Person@3ff2caf4====4

         po.Person@2c0cd7d====3

         */

        System.out.println("=====================================");

        Person person = new Person("张三", 11);

        Person person2 = new Person("张三", 11);

        System.out.println(person.equals(person2));

    }

}

package po;

/**

 * Created by Administrator on 2015/9/16.

 */

public class Person {

    int id;

    String name;

    int age;

    @Override

    public String toString() {

        return "Person{" +

                "id=" + id +

                ", name='" + name + '\'' +

                ", age=" + age +

                '}';

    }

    @Override

    public boolean equals(Object o) {

        if (this == o) return true;

        if (o == null || getClass() != o.getClass()) return false;

        Person person = (Person) o;

        if (id != person.id) return false;

        if (age != person.age) return false;

        return !(name != null ? !name.equals(person.name) : person.name != null);

    }

    @Override

    public int hashCode() {

        int result = id;

        result = 31 * result + (name != null ? name.hashCode() : 0);

        result = 31 * result + age;

        return result;

    }

    public Person(String name,int age){

        this.name=name;

        this.age=age;

    }

}