hashCode equals hashSet

基于hash的map也是这种机制。

HashSet

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

public class Sets {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Person p1 = new Person("320321");
        p1.setAge(22);
        p1.setName("p1");
        Person p2 = new Person("320321");
        p2.setAge(23);
        p2.setName("p2");
        Person p3 = new Person("320322");
        p3.setAge(22);
        p3.setName("p3");
        Person p4=new Person("320321");
        p4.setAge(22);
        p4.setName("p4");
        HashSet<Person> hashSet = new HashSet();
        /*
         * Add elements
         */
        // p1 equals p2, p1.hashCode != p2.hashCode
        hashSet.add(p1);
        hashSet.add(p2);
        // p1, p2
        System.out.println(hashSet);
        // p3 not equals p1, p2, but p3.hashCode == p1.hashCode
        hashSet.add(p3);
        // p1, p3, p2
        System.out.println(hashSet);
        // p4 equals p1, p2, and p4.hashCode == p1.hashCode
        hashSet.add(p4);
        // p1, p3, p2, without p4
        System.out.println(hashSet);
        
        /*
         * Remove elements. Now, the SET contains p1, p3, p2
         */
        hashSet.remove(p4);
        // p1 will be removed, since p1 equals p4 and p1.hashCode == p4.hashCode
        System.out.println(hashSet);
        // Although the SET contains p2 who equals p4, but can't find "p4"
        // Also, p3.hashCode == p4.hashCode but not find "p4" in the same bucket
        System.out.println(hashSet.contains(p4));
    }
}

Person

public class Person implements Comparable<Person> {
    private String name, id, gender;
    private int age;
    private String[] property;

    public Person() {
    }

    public Person(String id) {
        this.id = id;
    }

    public String getId() {
        return id;
    }

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

    public void setGender(String gender) {
        this.gender = gender;
    }

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

    public String getName() {
        return name;
    }

    public String getGender() {
        return gender;
    }

    public int getAge() {
        return age;
    }

    public String[] getProperty() {
        return property;
    }

    public void setProperty(String[] property) {
        this.property = property;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (!(o instanceof Person)) {
            return false;
        }
        Person p = (Person) o;
        if (id == null ? p.getId() == null : id.equals(p.getId())) {
            return true;
        }
        return false;
    }

    @Override
    public int hashCode() {
        return age;
    }

    @Override
    public String toString() {
        return this.id + "  age:  " + this.age + "  name:  " + this.name;
    }

    @Override
    public Person clone() {
        Person p = null;
        try {
            p = (Person) super.clone();
            p.setProperty(property.clone());
        } catch (CloneNotSupportedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return p;
    }

    @Override
    public int compareTo(Person p) {
        return this.age - p.getAge();
    }
}