Set集合

public class SetDemo {
    public static void main(String[] args) {
        //创建集合对象
        Set set=new HashSet<>();

        //添加元素
        set.add("hello");
        set.add("world");
        set.add("java");
        //不包含重复元素
        set.add("java");

        //遍历
        for (String s: set) {
            System.out.println(s);
        }
    }
}

public class Student {
    public String name;
    public int 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;
    }
 }

public class SetDemo2 {
    public static void main(String[] args) {
        //创建学生对象
        Student student=new Student();
        student.setAge(18);
        student.setName("lisi");

        //同一个对象多次调用hashCode()方法返回值是相同的
        System.out.println(student.hashCode());//460141958
        System.out.println(student.hashCode());//460141958

        Student student1=new Student();
        student1.setName("lisi");
        student1.setAge(18);
        //默认情况下,不同对象的哈希值不同(可以在Student类中重写hashCode()方法,这时候结果相同)
        System.out.println(student1.hashCode());//1163157884
        
        System.out.println("hello".hashCode());//99162322
        System.out.println("java".hashCode());//3254818
    }
}

想想为什么"java"和"hello"都有哈希值，并且不同(自己找资料查找)

public class HashSetDemo1 {
    public static void main(String[] args) {
        HashSet hashSet=new HashSet();

        //添加元素
        hashSet.add("hello");
        hashSet.add("world");
        hashSet.add("java");

        //遍历输出
        for (String s: hashSet) {
            System.out.println(s);
        }
    }
}

public class LinkedHashSetDemo {
    public static void main(String[] args) {
        LinkedHashSet list=new LinkedHashSet<>();

        //添加元素
        list.add("hello");
        list.add("world");
        list.add("java");
        list.add("java");

        System.out.println(list);
        for (String s: list) {
            System.out.println(s);
        }
    }
}

public class TreeSetDemo {
    public static void main(String[] args) {
        TreeSet set=new TreeSet<>();

        //添加元素
        set.add(10);
        set.add(25);
        set.add(14);
        set.add(14);

        System.out.println(set);
        for (Integer i: set) {
            System.out.println(i);
        }
    }
}

public class Student implements Comparable{
    public String name;
    public int age;
    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

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

    @Override
    public int compareTo(Object o) {
        return 1;
    }
}

public class TreeSetDemo2 {
    public static void main(String[] args) {
        //创建集合对象
        TreeSet set=new TreeSet();

        //创建学生集合对象
        Student student1=new Student("lisi",18);
        Student student2=new Student("zhangsan",20);
        Student student3=new Student("maliu",30);
        Student student4=new Student("wangwu",40);

        //把学生添加到集合中
        set.add(student1);
        set.add(student2);
        set.add(student3);
        set.add(student4);

        for (Student s: set) {
            System.out.println(s.getName()+","+s.getAge());
        }
    }
}

如果compareTo()方法返回的是0,则只打印一个结果
如果compareTo()方法返回的是-1,则逆着打印一个结果