1. 抽象类

抽象类定义之后不能被实例化，只能被继承，抽象方法定义之后，必须由继承类实现

abstract class Animal {name: string;constructor(name) {this.name = name;}abstract say():void
}class Dog extends Animal {constructor(name) {super(name);}say(): void {console.log('wangwang');}
}