5.class

一、 类

class Greeter {
    greeting: string;
    constructor(message: string) {
        this.greeting = message;
    }
    greet() {
        return "Hello, " + this.greeting;
    }
}

let greeter = new Greeter("world");
console.log(greeter.greet())

构造方法是 constructor

二、继承

class Animal {
    move(distanceInMeters: number = 0) {
        console.log(`Animal moved ${distanceInMeters}m.`);
    }
}

class Dog extends Animal {
    bark() {
        console.log('Woof! Woof!');
    }
}

const dog = new Dog();
dog.bark();
dog.move(10);
dog.bark();

super

如果父类的构造函数带参数，则子类调用父类构造函数时

class Animal {
    name: string;
    constructor(theName: string) { this.name = theName; }
    move(distanceInMeters: number = 0) {
        console.log(`${this.name} moved ${distanceInMeters}m.`);
    }
}

class Snake extends Animal {
    constructor(name: string) { super(name); }
    move(distanceInMeters = 5) {
        console.log("Slithering...");
        super.move(distanceInMeters);
    }
}

class Horse extends Animal {
    constructor(name: string) { super(name); }
    move(distanceInMeters = 45) {
        console.log("Galloping...");
        super.move(distanceInMeters);
    }
}

let sam = new Snake("Sammy the Python");
let tom: Animal = new Horse("Tommy the Palomino");

sam.move();
tom.move(34)

在构造函数里访问 ​​this​​的属性之前，我们 一定要调用 ​​super()​​

三、修饰符

public

在TypeScript里，成员都默认为 public

private

 不能在声明它的类的外部访问

class Animal {
    private name: string;
    constructor(theName: string) { this.name = theName; }
}
new Animal("Cat").name;  //报错

protected

 也不能在声明它的类的外部访问，但是可以在派生类中使用

class Animal {
    protected name: string;
    constructor(theName: string) { this.name = theName; }
}

class E extends Animal{
    //继承了父类name
    constructor(name: string) {super(name)}

    f(){ return 'f:'+this.name; }
}

let ee=new E('tom');
console.log(ee.f())

readonly

只读属性只能在声明时，或者构造函数里被初始化

class Octopus {
    readonly name: string;
    readonly numberOfLegs: number = 8;
    constructor (theName: string) {
        this.name = theName;
    }
}
let dad = new Octopus("Man with the 8 strong legs");
dad.name = "Man with the 3-piece suit"; // 错误! name 是只读的.

四、get set

class A {
    //
    private _n: number = 3;

    constructor(nn: number) { this.n = nn }

    //get属性
    get n() {
        return this._n;
    }
    //set属性
    set n(x: number) {
        if (x < 10) {
            this.n = x;
        } else {
            console.log('不能大于10');
        }
    }
}

let a = new A(20);

五、静态属性

class A {
    //
    static n: number = 3;
}

console.log(A.n)

六、抽象类

 抽象类不直接实例化，

abstract class A {
    //抽象方法
    abstract f1(): void;
    //普通方法
    f(): void { console.log('aa') }
}

class B extends A{
    //必须要实现父类的抽象类
    f1(){}
}