java二十三（Set）(HashSet、TreeSet、Lin

一、HashSet

• HashSet的父类为Set,特点是：
  1、没有顺序
  2、没有重复元素。
  3、没有下标，不能用for i 循环
• demo

 Dog dog1 = new Dog(1, "菲菲");
Set<Dog> dogSet = new HashSet<>();
        dogSet.add(dog1);
        dogSet.add(dog1);
//[Dog{age=1, name='菲菲'}],最后只打印一项
        System.out.println(Arrays.toString(dogSet.toArray()));

二、TreeSet

• TreeSet的父类为TreeSet,特点是：
  1、TreeSet对自定的Comparator元素比较进行排序输出
  2、Comparator元素比较进行排除重复元素
  3、没有下标，不能用for i 循环

 Dog dog1 = new Dog(1, "菲菲");
        Dog dog2 = new Dog(10, "哈皮");
        Dog dog3 = new Dog(100, "爷爷");
        Dog dog4 = new Dog(1, "Tom");
        Dog dog5 = new Dog(2, "哈皮");
// 对年龄进行排序
 TreeSet<Dog> dogTreeSet = new TreeSet<>(((d1, d2) -> d1.getAge() - d2.getAge()));
        dogTreeSet.add(dog1);
        dogTreeSet.add(dog2);
        dogTreeSet.add(dog3);
        dogTreeSet.add(dog4);
        dogTreeSet.add(dog5);

        // [Dog{age=1, name='菲菲'}, Dog{age=2, name='哈皮'}, Dog{age=10, name='哈皮'}, Dog{age=100, name='爷爷'}]
        System.out.println(Arrays.toString(dogTreeSet.toArray()));

三、LinkedHashSet

1、固定位置
2、没有重复元素。
3、没有下标，不能用for i 循环

 Dog dog1 = new Dog(1, "菲菲");
        Dog dog2 = new Dog(10, "哈皮");
        Dog dog3 = new Dog(100, "爷爷");
        Dog dog4 = new Dog(1, "Tom");
        Dog dog5 = new Dog(2, "哈皮");
 LinkedHashSet<Dog> dogLinkedHashSet = new LinkedHashSet<>();
        dogLinkedHashSet.add(dog1);
        dogLinkedHashSet.add(dog1);
        dogLinkedHashSet.add(dog2);
        dogLinkedHashSet.add(dog3);
        dogLinkedHashSet.add(dog4);
        dogLinkedHashSet.add(dog5);
        System.out.println(Arrays.toString(dogLinkedHashSet.toArray()));
//[Dog{age=1, name='菲菲'}, Dog{age=10, name='哈皮'}, Dog{age=100, name='爷爷'}, Dog{age=1, name='Tom'}, Dog{age=2, name='哈皮'}]

Dog.java

package com.kouding;

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

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

    public int getAge() {
        return age;
    }

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

    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;

        Dog dog = (Dog) o;

        if (age != dog.age) return false;
        return name.equals(dog.name);
    }

    @Override
    public String toString() {
        return "Dog{" +
                "age=" + age +
                ", name='" + name + '\'' +
                '}';
    }

    @Override
    public int hashCode() {
        int result = age;
        result = 31 * result + name.hashCode();
        return result;
    }
}