案例:HashMap集合存储学生对象并遍历

需求:创建一个HashMap集合，键是学生对象,值是居住地,存储对个键值对元素,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,我们就认为同一对象 思路:

1. 定义学生类
2. 创建HashMap集合
3. 创建学生对象
4. 把学生对象添加到集合中
5. 遍历集合: 方式1:键找值 方式2:键值对对象找键和值
6. 在学生类中重写方法 hashCode() equals()

注意:hashMap底层结构是哈希值，重写相应的方法可以保键的唯一性(注意是键的唯一性)

以代码的内容形式展开

Student类(注意有重写方法)

package Demo;

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);
    }
}

Demo类

package Demo;

import java.util.*;

public class Demo {
          
   
    public static void main(String[] args) {
          
   
        //创建HashMap()
        HashMap<Student, String> s = new HashMap<>();

        //建立集合
        Student s1 = new Student("沸羊羊",21);
        Student s2 = new Student("喜羊羊",23);
        Student s3 = new Student("懒洋洋",19);
        Student s4 = new Student("美羊羊",27);
        Student s5 = new Student("美羊羊",27);

        //添加元素
        s.put(s1,"西安");
        s.put(s2,"汉中");
        s.put(s3,"榆林");
        s.put(s4,"咸阳");
        s.put(s5,"咸阳");

        //遍历集合
        //1    根据键所找值
        Set<Student> students = s.keySet();
        for (Student x:students) {
          
   
            String sss = s.get(x);
            System.out.println(x.getName()+","+x.getAge()+","+sss);
        }

        System.out.println("================");
        //2    根据键对所找值
        Set<Map.Entry<Student, String>> entries = s.entrySet();
        for (Map.Entry<Student, String> x:entries) {
          
   
            Student key = x.getKey();
            String value = x.getValue();
            System.out.println(key.getName()+ key.getAge()+","+value);
        }


    }
}

输出的内容 喜羊羊,23,汉中 沸羊羊,21,西安 美羊羊,27,咸阳 懒洋洋,19,榆林

================

喜羊羊23,汉中 沸羊羊21,西安 美羊羊27,咸阳 懒洋洋19,榆林