JAVA单排日记-2020/1/1-1-Set接口元素不重复原理

import java.util.HashSet;

public class DemoHashSet {
    public static void main(String[] args) {
        HashSet<String> str = new HashSet<>();

        str.add("asd");
        str.add("asd");
        str.add("重地");
        str.add("通话");
    }
}

• 使用HashSet存储自定义类型元素时，要重写hashCode()和equals方法，不然会保存重复元素

如：没有覆盖重写

import java.util.Objects;

public class Person {
    String name;
    int age;

    public Person() {
    }

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

    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;
    }

     重写toString可以打印输出内容而不是地址值
    @Override 
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

import java.util.HashSet;

public class Demoperson {
    public static void main(String[] args) {
        HashSet<Person> one = new HashSet<>();

        Person a1 = new Person("一号",18);
        Person a2 = new Person("二号",18);
        Person a3 = new Person("一号",18);

        one.add(a1);
        one.add(a2);
        one.add(a3);

        System.out.println(one);

    }
}

重写hashCode()和equals方法

import java.util.Objects;

public class Person {
    String name;
    int age;

    public Person() {
    }

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

    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 +
                '}';
    }

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

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

import java.util.HashSet;

public class Demoperson {
    public static void main(String[] args) {
        HashSet<Person> one = new HashSet<>();

        Person a1 = new Person("一号",18);
        Person a2 = new Person("二号",18);
        Person a3 = new Person("一号",18);

        one.add(a1);
        one.add(a2);
        one.add(a3);

        System.out.println(one);

    }
}