[数据结构与算法]javaSE关于HashMap的笔记（2）

1.创建学生类

package bean;

import java.util.Objects;

public class Student {
    // 属性
    private String name;

    // 构造方法
    public Student() {
    }
    public Student(String name) {
        this.name = name;
    }

    // getter and setter
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return Objects.equals(name, student.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name);
    }
}

2.测试数据

package collection;

import bean.Student;

import java.util.HashSet;
import java.util.Set;

public class HashMapTest02 {
    public static void main(String[] args) {
        bean.Student s1 = new Student("zhangsan");
        bean.Student s2 = new Student("zhangsan");

        // 重写equals方法之前是false
        //System.out.println(s1.equals(s2)); // false

        // 重写equals方法之后是true
        System.out.println(s1.equals(s2)); // true

        System.out.println("s1的hashCode=" + s1.hashCode());
        System.out.println("s1的hashCode=" + s2.hashCode());
        Set<bean.Student> students = new HashSet<>();
        students.add(s1);
        students.add(s2);
        System.out.println(students.size()); // hashCode方法重写前是2，重写后是1
    }
}