30.6 HashMap的使用

/*
*
* 使用HashMap存储数据并遍历（字符串作为key）
*
*使用HashMap存储数据并遍历（自定义对象作为key）
*/

字符串做key和Map的使用一样，重点介绍自定义对象作为key

package day30_2_Map.hashmap;

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

/*
 * 使用HashMap存储数据并遍历（自定义对象作为key）
 */
public class HashMapDemo2 {
    public static void main(String[] args) {
        HashMap<Student,String> hm = new HashMap<>();

        Student s = new Student("zhangsan",12);
        Student s2 = new Student("lisi",18);
        Student s3 = new Student("lisi",18);

        hm.put(s,"test001");
        hm.put(s2,"test002");
        hm.put(s3,"test002");

        Set<Map.Entry<Student,String>> entry = hm.entrySet();
        for (Map.Entry<Student,String> entrys : entry) {
            Student key = entrys.getKey();
            String value = entrys.getValue();
            System.out.println(key + "=" +value);
        }

    }
}

package day30_2_Map.hashmap;

import jdk.net.SocketFlow;

import java.util.Objects;

public class Student {
    String name;
    int age;

    public Student() {
    }

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

    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }

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

    @Override
    public int hashCode() {

        return Objects.hash(name, age);
    }
}

输出

说明：

输出Student对象为地址值，需要重写其toString方法

作为key的Student对象未去重，需要重新equals和hashcode方法