【HashMap集合】存储学生对象并遍历

news2024/11/15 9:16:58

HashMap集合存储学生对象并遍历

1.键是String，值是Student

需求：创建一个HashMap集合，键是学号(String)，值是学生对象(Student)。存储三个键值对元素，并遍历

思路：

定义学生类

创建HashMap集合对象

创建学生对象

把学生添加到集合

遍历集合

方式1：键找值

方式2：键值对对象找键和值

学生类：

package com.gather.map.example;
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;
    }
}

测试类：

package com.gather.map.example;
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<String, Student> hm = new HashMap<String, Student>();
        //创建学生对象
        Student s1 = new Student("郝佳乐", 20);
        Student s2 = new Student("张三", 18);
        Student s3 = new Student("李四", 22);
        //把学生添加到集合
        hm.put("student001", s1);
        hm.put("student002", s2);
        hm.put("student003", s3);
        //遍历集合
        //方式1：键找值
        //获取所有键的集合
        Set<String> keySet = hm.keySet();
        for (String key : keySet) {
            Student value = hm.get(key);
            System.out.println(key + "," + value.getName() + "," + value.getAge());
        }
        System.out.println("=======================");
        //方式2：键值对对象找键和值
        Set<Map.Entry<String, Student>> entrySet = hm.entrySet();
        //获取所有的键值对对象
        for (Map.Entry<String, Student> me : entrySet) {
            String key = me.getKey();
            Student value = me.getValue();
            System.out.println(key + "," + value.getName() + "," + value.getAge());
        }
    }
}

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2.键是学生对象，值是居住地

需求：创建一个HashMap集合，键是学生对象(Student)，值是居住地(String)。存储多个键值对元素，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

思路：

定义学生类

创建HashMap集合对象

创建学生对象

把学生添加到集合

遍历集合

在学生类中重写两个方法

hashCode()

equals()

学生类：

package com.gather.map.example;
public class Student1 {
    private String name;
    private int age;

    public Student1() {
    }

    public Student1(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;

        Student1 student1 = (Student1) o;

        if (age != student1.age) return false;
        return name != null ? name.equals(student1.name) : student1.name == null;
    }

    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;
    }
}

测试类：

package com.gather.map.example;
import java.util.HashMap;
import java.util.Set;
public class HashMapDemo01 {
    public static void main(String[] args) {
        HashMap<Student1, String> hm = new HashMap<Student1, String>();
        Student1 s1 = new Student1("郝佳乐", 20);
        Student1 s2 = new Student1("张三", 18);
        Student1 s3 = new Student1("李四", 22);
        Student1 s4 = new Student1("李四", 22);
        hm.put(s1, "西安");
        hm.put(s2, "武汉");
        hm.put(s3, "郑州");
        hm.put(s4, "北京");
        //遍历集合
        Set<Student1> keySet = hm.keySet();
        for (Student1 key : keySet) {
            String value = hm.get(key);
            System.out.println(key.getName() + "," + key.getAge() + "," + value);
        }
    }
}