JavaSE-15.1.4【案例-HashSet集合存储学生对象并遍历】

package day6.lesson1;

import java.util.HashSet;

/*
1.6 案例-HashSet集合存储学生对象并遍历

    创建一个存储学生对象的集合，存储多个学生对象，使用程序实现在控制台遍历该集合
    要求：学生对象的成员变量值相同，我们就认为是同一个对象

 */
public class HashSetDemo4 {
    public static void main(String[] args) {
        HashSet<Student> hs = new HashSet<>();

        Student s1 = new Student("tom", 22);
        Student s2 = new Student("sam", 23);
        Student s3 = new Student("amy", 21);
        Student s4 = new Student("amy", 21);

        hs.add(s1);
        hs.add(s2);
        hs.add(s3);
        hs.add(s4);

        for (Student s: hs){
            System.out.println(s.getName() + "," + s.getAge());
        }
        /*
        Student类重写equals()和hashCode()之前输出：
        sam,23
        amy,21
        tom,22
        amy,21

        为保证元素唯一性，Student类重写equals()和hashCode()两个方法（alt+insert自动生成）

        Student类重写equals()和hashCode()之后输出：
        tom,22
        amy,21
        sam,23amy,21
        sam,23
         */
    }
}

 

package day6.lesson1;

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;
    }

    //HashDemo2.java
    /*@Override
    public int hashCode() {
//        return super.hashCode(); //默认
        return 0; //此时可以实现让不同对象的哈希值相同
    }*/

    //HashSetDemo4.java
    @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;
    }
}