java中map插入相同的key

朴灿烈づ我的快乐病毒、 2022-07-16 07:18 191阅读 0赞

测试用例：

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;
        }
    }