多态的形成有3个条件

1. 有继承
2. 有重写
3. 有父类对象指向子类引用

多态形式

向上转型 父类 父类对象 = new 子类();
向下转型 要先发生向上转型，才能通过强转再转成子类类型

instanceof 关键字

判断第一个对象是否是某一个类的东西

if(animal instanceof Cat) {
    Cat cat = new Cat();
    cat.catchMouse();
}else if (animal instanceof Dog) {
    Dog dog = new Dog();
    dog.look();
} else {
    code;
}

匿名对象

语法:new 类名();
功能：和正常有名字的对象的功能是相同的，依然具备了调用属性、方法的功能
使用场景：多数是用在传参、夹参，多数情况下配合构造器使用
好处：节约资源，栈的资源

程序运用

Person类（构造器）

public class Person {

    private String name;
    private Integer age;

    public Person() {

    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

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

Student类

public class Student extends Person{
    public Student() {
    }

    public Student(String name, Integer age) {
        super(name, age);
    }
}

Teahcer类

public class Teacher extends Person{
    public Teacher() {
        super();
    }

    public Teacher(String name, Integer age) {
        super(name, age);
    }
}

School类（操作）

public class School {

    public void start(Person person) {
        if (person instanceof Teacher) {
            System.out.println(person.getAge() + "岁的" + person.getName() + "老师开学去办公楼");
        } else if (person instanceof  Student) {
            System.out.println(person.getAge() + "岁的" + person.getName() + "学生开学去寝室楼");
        }
    }

    public void end(Person person) {
        if (person instanceof Teacher) {
            System.out.println(person.getAge() + "岁的" + person.getName() + "老师放学去逛街了");
        } else if (person instanceof  Student) {
            System.out.println(person.getAge() + "岁的" + person.getName() + "学生放学坐车回家");
        }
    }

    public static void main(String[] args) {
        School school = new School();
        Teacher teacher = new Teacher("王老师",43);
        Student student = new Student("小明",21);

        school.start(teacher);
        school.start(student);
        school.end(teacher);
        school.end(student);
    }
}