类

继承

class Animal {
    name: string;
    constructor(theName: string) { this.name = theName; }
    // 方法的默认参数
    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...");
        // 重写从父类继承的方法
        super.move(distanceInMeters);
    }
}

class Horse extends Animal {
    constructor(name: string) {
        // 在使用this之前，一定要先调用父类的super()方法
        super(name);
    }
    move(distanceInMeters = 45) {
        console.log("Galloping...");
        // 重写从父类继承的方法
        super.move(distanceInMeters);
    }
}
let sam = new Snake("Sammy the Python");
// 声明tom为Animal类，但是new的是Horse类 
let tom: Animal = new Horse("Tommy the Palomino");
sam.move();
// 调用的依然是Horse类的move方法
tom.move(34);

理解public , private , protected

public

1. 在TypeScript里，成员都默认为 public 。 你也可以明确的将一个成员标记成 public

理解private

1. 当成员被标记成 private 时，它就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; // 错误: 'name' 是私有的.

理解protected

protected 修饰符与 private 修饰符的行为很相似，但有一点不同， protected 成员在派生类中仍然可以访问。

class Person {
    protected name: string;
    constructor(name: string) { this.name = name }
}
class Employee extends Person {
    private department: string;
    constructor(name: string, department: string) {
        super(name)
        this.department = department
    }
    public getElevatorPitch() {
        // 不能在 Person 类外使用 name ，但是我们仍然可以通过 Employee 类的实例方法访问，
        // 因为 Employee 是由 Person 派生而来的
        return `hello,my name is ${this.name} and i work in ${this.department}`
    }
}
let howard = new Employee("Howard", "Sales");
console.log(howard.getElevatorPitch());
// name被标记为protected在类的外部不可以访问
console.log(howard.name); // 错误

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构造函数被标记为protected

构造函数也可以被标记成 protected 。 这意味着这个类不能在包含它的类外被实例化，但是能被继承

class Person {
    protected name: string;
    // 构造函数被标记为protected
    protected constructor(theName: string) { this.name = theName; }
}
// Employee 能够继承 Person 
class Employee extends Person {
    private department: string;
    constructor(name: string, department: string) {
        super(name);
        this.department = department;
    }
    public getElevatorPitch() {
        return `Hello, my name is ${this.name} and I work in ${this.department}.`;
    }
}
let howard = new Employee("Howard", "Sales");
let john = new Person("John"); // 错误: 'Person' 的构造函数是被保护的
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