Java中的HashSet、LinkedHashSet集合解析

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
        boolean r1 = s.add("朵朵");
        boolean r2 = s.add("朵朵");
        //true
        System.out.println(r1);
        //false
        System.out.println(r2);
        //[朵朵]
        System.out.println(s);
        boolean r3 = s.add("小七");
        boolean r4 = s.add("钢镚");
        //无序
        //[钢镚, 朵朵, 小七]
        System.out.println(s);
        //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);
        }
        //Lambda
        s.forEach(str -> System.out.println(str));
    }
}

public class A02_HashSetDemo1 {
    public static void main(String[] args) {
        //1。创建对象
        Student s1 = new Student("朵朵", 5);
        Student s2 = new Student("朵朵", 5);
        //2。 如果没有重写hashCode方法，不同对象计算出的哈希值是不同的
        //1554874502
        System.out.println(s1.hashCode());
        //1846274136
        System.out.println(s2.hashCode());
        //重写hashCode后：不同的对象只要属性值相同，计算出的哈希值就是一样的
        //26209637
        System.out.println(s1.hashCode());
        //26209637
        System.out.println(s2.hashCode());
        //3。在小部分情况下，不同的属性值或者不同地址值计算出来的哈希值也可能一样（哈希碰撞）
        //96354
        System.out.println("abc".hashCode());
        //96354
        System.out.println("acD".hashCode());
    }
}

public class A02_HashSetDemo2 {
    public static void main(String[] args) {
        //1。创建3个学生对象
        Student s1 = new Student("朵朵", 5);
        Student s2 = new Student("小七", 7);
        Student s3 = new Student("钢镚", 9);
        Student s4 = new Student("朵朵", 5);
        //2。创建集合用来添加学生
        HashSet<Student> hs = new HashSet<>();
        //3。添加元素（重写hashCode和equal方法后）
        //true
        System.out.println(hs.add(s1));
        //true
        System.out.println(hs.add(s2));
        //true
        System.out.println(hs.add(s3));
        //false
        System.out.println(hs.add(s4));
        //4。打印集合
        //[Student{name = 小七, age = 7}, Student{name = 钢镚, age = 9}, Student{name = 朵朵, age = 5}]
        System.out.println(hs);
    }
}

public class A04_LinkedHashSetDemo {
    public static void main(String[] args) {
        //1。创建3个学生对象
        Student s1 = new Student("朵朵", 5);
        Student s2 = new Student("小七", 7);
        Student s3 = new Student("钢镚", 9);
        Student s4 = new Student("朵朵", 5);

        //2。创建集合用来添加学生
        LinkedHashSet<Student> lhs = new LinkedHashSet<>();

        //3。添加元素（重写hashCode和equal方法后）
        //true
        System.out.println(lhs.add(s1));
        //true
        System.out.println(lhs.add(s2));
        //true
        System.out.println(lhs.add(s3));
        //false
        System.out.println(lhs.add(s4));

        //4。打印集合
        //与添加顺序一样
        //[Student{name = 朵朵, age = 5}, Student{name = 小七, age = 7}, Student{name = 钢镚, age = 9}]
        System.out.println(lhs);
    }
}