HashMap存储自定义类型键值

• HashMap存储自定义类型键值
• Map集合保证key是唯一的：作为key的元素，必须重写hashCode方法和equals方法，以保证key唯一

package collection;

import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.Set;

public class Demo01HashMapSavePerson {

    public static void main(String[] args) {
        show01();
        System.out.println("==================");
        show02();
    }

    private static void show02() {
        HashMap map = new HashMap<>();

        map.put(new Person("女王", 18), "英国");
        map.put(new Person("秦始皇", 18), "泰国");
        map.put(new Person("普京", 30), "俄罗斯");
        map.put(new Person("女王", 18), "毛里求斯");

        Set> set = map.entrySet();
        for (Map.Entry entry : set) {
            Person key = entry.getKey();
            String value = entry.getValue();
            System.out.println(key + "-->" + value);
        }
    }

    private static void show01() {

        HashMap map = new HashMap<>();

        map.put("北京", new Person("张三", 18));
        map.put("广州", new Person("李四", 19));
        map.put("广东", new Person("王五", 20));
        map.put("北京", new Person("赵六", 21));

        Set set = map.keySet();
        for (String key : set) {
            Person value = map.get(key);
            System.out.println(key + "-->" + value);
        }
    }
}

class Person {
    private String name;
    private int age;

    public Person() {
    }

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public boolean equals(Object object) {
        if (this == object) return true;
        if (object == null || getClass() != object.getClass()) return false;
        Person person = (Person) object;
        return age == person.age && Objects.equals(name, person.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}
D:\Java\jdk-17\bin\java.exe "-javaagent:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\lib\idea_rt.jar=13388:D:\BaiduNetdiskDownload\IntelliJ IDEA 2023.2\bin" -Dfile.encoding=UTF-8 -classpath F:\IdeaProjects\JavaSenior\out\production\Test;D:\develop\maven\repository\junit\junit\4.13.1\junit-4.13.1.jar;D:\develop\maven\repository\org\hamcrest\hamcrest-core\1.3\hamcrest-core-1.3.jar collection.Demo01HashMapSavePerson
广州-->Person{name='李四', age=19}
广东-->Person{name='王五', age=20}
北京-->Person{name='赵六', age=21}
==================
Person{name='女王', age=18}-->毛里求斯
Person{name='秦始皇', age=18}-->泰国
Person{name='普京', age=30}-->俄罗斯

Process finished with exit code 0

1、HashMap集合的特点

• 元素按照键是无序，不重复，无索引，值不做要求。