export class Animal {
    
    public say():void{
        console.log("I am a Animal");
    }
}

export class Dog extends Animal {
    
    public override say():void{
        console.log("I am a Dog");
    }
}

let animal: Animal = new Dog();
animal.say(); // output: I am a Dog

let dog: Dog = new Dog();
dog.say();// output: I am a Dog

• 当子类方法的名称、参数、返回值都相同时，则视为覆盖基类的方法，override 关键字可以省略