Set集合存储元素不重复的原理和HashSet存储自定义类型元素

Set集合存储元素不重复的原理

 

 

 

 

HashSet存储自定义类型元素

给HashSet中存放自定义类型元素时，需要重写对象中的hashCode和equals方法，建立自己的比较方式，才能保 证HashSet集合中的对象唯一

Hashset存储自定义类型元素

　　set集合报错元素唯一:
　　　　存储的元素(String, Integer, . . .Student , Person...) ,必须重写hashCode方法和equals

方法要求:
　　同名同年龄的人,视为同一个人,只能存储一次

public class Person {
    private String name;
    private int age;

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

    public Person() {
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

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

 

public static void main(String[] args) {
        //创建Hashset集百仔1储Person
        HashSet<Person> set = new HashSet<>();
        Person p1 = new Person("哦", 18);
        Person p2 = new Person("嗯", 18);
        Person p3 = new Person( "哦", 19);
        System.out.println(p1.hashCode());

         System.out.println(p2.hashCode());
        System.out.println(p1==p2);


        System.out. println(p1.equals(p2));
        set.add(p1);
        set.add(p2);
        set.add(p3);
        System.out.println(set) ;

    }

 

public class Person {
    private String name;
    private int age;
    public Person() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Person(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }
    
    @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;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    @Override
        public String toString() {
        return "Person [name=" + name + ", age=" + age + "]";
    }
}

public class Demo03HashSetSavePerson {
    public static void main(String[] args) {
        //创建HashSet集合存储Person
        HashSet<Person> set = new HashSet<>();
        Person p1 = new Person("张伟", 18);
        Person p2 = new Person("张伟", 18);
        Person p3 = new Person("张伟", 18);
        System.out.println(p1.hashCode());//776686
        System.out.println(p2.hashCode());//776686
        System.out.println(p1 == p2);//false
        System.out.println(p1.equals(p2));//true
        set.add(p1);
        set.add(p2);
        set.add(p3);
        System.out.println(set);//[Person [name=张伟, age=18]]
    }
}