Set

package com.text.entity;

import java.util.*;
import java.util.function.Consumer;

public class A01_SetDemo1 {
    public static void main(String[] args) {
        //1. 创建一个Set集合的对象
        Set<String> s = new HashSet<>();

        // 2. 添加元素
        // 如果当前元素是第一次添加，那么可以添加成功，返回true
        // 如果当前元素是第二次添加，那么添加失败，返回false
        s.add("张三");
        s.add("张三");
        s.add("李四");
        s.add("王五");

        // 打印集合
        // 无序
        //System.out.println(s); // [李四, 张三, 王五]

        //迭代器遍历
        /*Iterator<String> it = s.iterator();
        while (it.hasNext()) {
            String str = it.next();
            System.out.println(str);
        }*/

        // 增强for
        /*for (String str : s) {
            System.out.println(str);
        }*/

        //lambad 表达式遍历
        s.forEach(str -> System.out.println(str));
    }
}

Student 类

package com.text.entity;

import java.util.Objects;

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


    public Student() {
    }

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

    /**
     * 获取
     * @return name
     */
    public String getName() {
        return name;
    }

    /**
     * 设置
     * @param name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * 获取
     * @return age
     */
    public int getAge() {
        return age;
    }

    /**
     * 设置
     * @param age
     */
    public void setAge(int age) {
        this.age = age;
    }

    public String toString() {
        return "Student{name = " + name + ", age = " + age + "}";
    }

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

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

HashSet

Demo1

package com.text.entity;

public class A02_ShashSetDemo1 {
    public static void main(String[] args) {
        //1. 创建对象
        Student s1 = new Student("zhangsan", 23);
        Student s2 = new Student("zhangsan", 21);

        // 如果没有重写hashCode方法，不同对象计算出的哈希值是不同的
        System.out.println(s1.hashCode()); // -1461067292
        System.out.println(s2.hashCode()); // -1461067292

        // 哈希碰撞
        System.out.println("abc".hashCode()); // 96354
        System.out.println("acD".hashCode()); // 96354
    }
}

Demo2

package com.text.entity;

import java.util.HashMap;
import java.util.HashSet;

public class A03_HashSetDemo2 {
    public static void main(String[] args) {

        // 1. 创建三个学生对象
        Student s1 = new Student("zhangsan", 23);
        Student s2 = new Student("lisi", 24);
        Student s3 = new Student("wangwu", 25);
        Student s4 = new Student("zhangsan", 23);

        // 2. 创建集合用来添加学生
        HashSet<Student> hs = new HashSet<>();

        // 3. 添加元素
        System.out.println(hs.add(s1));
        System.out.println(hs.add(s2));
        System.out.println(hs.add(s3));
        System.out.println(hs.add(s4));

        // 4. 打印集合
        System.out.println(hs);
    }
}

LinkedHashSet

package com.text.entity;

import sun.awt.image.ImageWatched;

import java.util.LinkedHashMap;
import java.util.LinkedHashSet;

public class A04_LinkedHashSetDemo {
    public static void main(String[] args) {
        // 1. 创建4个学生对象
        Student s1 = new Student("zhangsan", 23);
        Student s2 = new Student("lisi", 24);
        Student s3 = new Student("wangwu", 25);
        Student s4 = new Student("zhangsan", 23);



        // 2. 创建集合的对象
        LinkedHashSet<Student> lhs = new LinkedHashSet<>();

        // 3.添加元素
        System.out.println(lhs.add(s1));
        System.out.println(lhs.add(s2));
        System.out.println(lhs.add(s3));
        System.out.println(lhs.add(s4));

        // 4. 打印集合（按照添加的顺序）
        System.out.println(lhs);
    }
}

    对于HashSet和LinkedHashSet的选择问题：
1. 默认使用HashSet
2. 如果要求去重且有序，才使用LinkedHashSet