HashMap使用

当给HashMap中存放自定义对象时，如果自定义对象作为key存在，这时要保证对象唯一，必须复写对象的hashCode和equals方法(如果忘记，请回顾HashSet存放自定义对象)。

package MONA.demo01;

import java.util.HashMap;
import java.util.Objects;

/**
 * 自定义对象作为Kkey
 * 当自定义对象作为key时，自定义对象必须重写一下两个方法
 * hashCode
 * equals
 */
public class Demo04 {
    public static void main(String[] args) {
        //key是唯一的
        //HashMap所有的数据结构针对的都是key
        HashMap<Student,String> hashMap = new HashMap<>();
        hashMap.put(new Student("李四",19),"aaa");
        hashMap.put(new Student("王五",20),"bbb");
        hashMap.put(new Student("赵六",21),"ccc");
        hashMap.put(new Student("赵六",21),"ccc");

        System.out.println("hashMap"+hashMap);
    }
}
class Student{
    private String name;
    private int age;

    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);
    }
}