HashSet은 어떻게 요소가 중복되지 않도록 합니까?

package com.melody.bean;
public class Person {
    private String name;
    private int age;
    /**
     *
     */
    public Person() {
        super();

    }
    /**
     * @param name
     * @param age
     */
    public Person(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    /**
     * @return the name
     */
    public String getName() {
        return name;
    }
    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
    /**
     * @return the age
     */
    public int getAge() {
        return age;
    }
    /**
     * @param age the age to set
     */
    public void setAge(int age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + "]";
    }
    /**
     *     31?
     * 1.31     ,     1         
     * 2.31       
     * 3.31     2 5  -1,2      
     */
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + age;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Person other = (Person) obj;
        if (age != other.age)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }

}

package com.melody.set;

import java.util.HashSet;

import com.melody.bean.Person;

public class Demo1_HashSet {
    /**
     * @param args
     * Set  ,   ,     ,  (     )
     */
    public static void main(String[] args) {
//        test1();
        HashSet hs = new HashSet<>();
        hs.add(new Person("  ", 23));
        hs.add(new Person("  ", 24));
        hs.add(new Person("  ", 23));
        hs.add(new Person("  ", 24));
        hs.add(new Person("  ", 23));

        //         ,     ,    HashCode equals  
        System.out.println(hs.size());
        System.out.println(hs);
    }

    private static void test1() {
        HashSet hs = new HashSet<>();
        hs.add("ce");
        boolean b1 = hs.add("a");
//        boolean b2 = hs.add("a");
        hs.add("b");
        hs.add("c");
        hs.add("d");
        //HashSet   set            false
        //HashSet          set  
//        System.out.println("b1 ＝ " + b1 + " b2 = " + b2);
        System.out.println(hs);

        //               for  
        for (String string : hs) {
            System.out.println(string);
        }
    }

}