JavaSE-16.1.2【案例-HashMap集合存储学生对象并遍历*2】

package day7.lesson1.anli1;

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

/*
1.5 Map集合的案例

1.5.1 案例-HashMap集合存储学生对象并遍历#1
    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
 */
public class HashMapDemo {
    public static void main(String[] args) {
        HashMap<String, Student> map = new HashMap<>();

        Student s1 = new Student("zhangsan" , 12);
        Student s2 = new Student("lisi" , 14);
        Student s3 = new Student("wangwu" , 12);

        map.put("itheima01", s1);
        map.put("itheima02", s2);
        map.put("itheima03", s3);

        Set<String> keySet = map.keySet();
        for (String id: keySet){
            Student stu = map.get(id);
            System.out.println("学号：" + id + ", 姓名：" + stu.getName() + "， 年龄：" + stu.getAge());
        }
        /*
        学号：itheima01, 姓名：zhangsan， 年龄：12
        学号：itheima02, 姓名：lisi， 年龄：14
        学号：itheima03, 姓名：wangwu， 年龄：12
         */

        System.out.println();
        Set<Map.Entry<String, Student>> entrySet = map.entrySet();
        for (Map.Entry<String, Student> me: entrySet){
            String id = me.getKey();
            Student stu = me.getValue();
            System.out.println("学号：" + id + ", 姓名：" + stu.getName() + "， 年龄：" + stu.getAge());
        }
    }
}

package day7.lesson1.anli1;

public class Student {

    private String name;
    private int age;

    public Student() {
    }

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

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

package day7.lesson1.anli2;

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

/*
1.5.2 案例-HashMap集合存储学生对象并遍历#2
    创建一个HashMap集合，键是学生对象(Student)，值是居住地 (String)。存储多个元素，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
                       学生类中重写hashCode() & equels()
 */
public class HashMapDemo {
    public static void main(String[] args) {
        HashMap<Student, String> hm = new HashMap<>();

        Student s1 = new Student("zhangsan", 12);
        Student s2 = new Student("lisi", 14);
        Student s3 = new Student("wangwu", 12);
        Student s4 = new Student("wangwu", 12);

        hm.put(s1, "北京");
        hm.put(s2, "上海");
        hm.put(s3, "南京");
        hm.put(s4, "武汉");

        Set<Student> keySet = hm.keySet();
        for (Student student: keySet){
            String address = hm.get(student);
            System.out.println("姓名：" + student.getName() + ", 年龄：" + student.getAge() + ", 地址：" + address);
        }
        /*
        //学生类中重写hashCode() & equels()之前：
        姓名：lisi, 年龄：14, 地址：上海
        姓名：wangwu, 年龄：12, 地址：武汉
        姓名：zhangsan, 年龄：12, 地址：北京
        姓名：wangwu, 年龄：12, 地址：南京

        //学生类中重写hashCode() & equels()之后：
        姓名：zhangsan, 年龄：12, 地址：北京
        姓名：wangwu, 年龄：12, 地址：武汉  //值（address）被覆盖了
        姓名：lisi, 年龄：14, 地址：上海
         */

        System.out.println();
        Set<Map.Entry<Student, String>> entrySet = hm.entrySet();
        for (Map.Entry<Student, String> me: entrySet){
            Student student = me.getKey();
            String address = me.getValue();
            System.out.println("姓名：" + student.getName() + ", 年龄：" + student.getAge() + ", 地址：" + address);
        }
    }
}

package day7.lesson1.anli2;

public class Student {

    private String name;
    private int age;

    public Student() {
    }

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

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Student student = (Student) o;

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

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