创建一个HashMap集合，键是学生对象(Student)，值是居住地 (String)。存储四个键值对元素，并遍历。要求保证键的唯一性：如果学生对象的成员变量值相同，我们就认为是同一个对象

//学生类
//注意：需要重写两个方法hashCode()和equals()
package package6;

import java.util.Objects;

public class Student {
    private String name;
    private int age;

    public Student() {
    }

    public Student(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 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);
    }
}

//测试类
package package6;

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

public class HashMapDemo {
    public static void main(String[] args) {
        //创建HashMap集合对象
        HashMap<Student, String> hashMap = new HashMap<>();
        //创建学生对象
        Student s1 = new Student("张三", 21);
        Student s2 = new Student("李四", 22);
        Student s3 = new Student("王五", 23);
        Student s4 = new Student("王五", 23);
        //将学生对象存储到集合中
        hashMap.put(s1,"安庆");
        hashMap.put(s2,"南京");
        hashMap.put(s3,"合肥");
        hashMap.put(s4,"芜湖");


        //遍历集合
        Set<Map.Entry<Student, String>> entrySet = hashMap.entrySet();
        for(Map.Entry<Student, String> me:entrySet){
            Student key = me.getKey();
            String value = me.getValue();
            System.out.println(key.getName()+", "+key.getAge()+", "+value);
        }
    }
}

运行结果

张三, 21, 安庆
李四, 22, 南京
王五, 23, 芜湖