分享程序员开发的那些事...
更新时间：2022-09-21 19:11:08
测试用例：
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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));
}
} |
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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;
}
} |
本文转自Ryan.Miao博客园博客，原文链接：http://www.cnblogs.com/woshimrf/p/4813664.html，如需转载请自行联系原作者