Abstract classes and subclasses problem parent class

Date: 2020/1/14

Abstract classes and subclasses of the parent class problem: Function

IDE：Intellij IDEA

When the abstract class methods, class must be abstract.
Subclass inherits all abstract methods abstract class must override, otherwise, the subclass is also abstract class
abstract class can not be instantiated, it must be inherited by subclasses and override methods

package testDemo;

abstract class Animal{
    abstract public void eat();
}

class Dog extends Animal{

    @Override
    public void eat() {
        System.out.println("小狗吃东西");
    }
}

class Cat extends Animal{

    @Override
    public void eat() {
        System.out.println("小猫吃东西");
    }
}

public class BackAnimal {
    public static void main(String[] args){
        Animal animal;
        animal = new Dog();
        animal.eat();
        animal = new Cat();
        animal.eat();
    }
}