抽象类

abstract class Machine {
    constructor(public manufacturer: string) {
    }

    // An abstract class can define methods of it's own, or...
    summary(): string {
        return `${this.manufacturer} makes this machine.`;
    }
    
    // Require inheriting classes to implement methods
    abstract moreInfo(): string;
}

class Car extends Machine {
    constructor(manufacturer: string, public position: number, protected speed: number) {
        super(manufacturer);
    }
    
    move() {
        this.position += this.speed;
    }
    
    moreInfo() {
        return `This is a car located at ${this.position} and going ${this.speed}mph!`;
    }
}

let myCar = new Car("Konda", 10, 70);
myCar.move(); // position is now 80
console.log(myCar.summary()); // prints "Konda makes this machine."
console.log(myCar.moreInfo()); // prints "This is a car located at 80 and going 70mph!"

抽象类是其他类可以扩展的基类。他们不能自己实例化（即你不能做 new Machine("Konda")）。

Typescript 中抽象类的两个关键特征是：

1. 他们可以实现自己的方法。
2. 他们可以定义继承类必须实现的方法。

因此，抽象类在概念上可以被视为接口和类的组合。