1-5，类

使用class申明

一、继承

class Animal { // 基类
    name: string;
    constructor(theName: string) { this.name = theName; }
    move(distanceInMeters: number = 0) {
        console.log(`${this.name} moved ${distanceInMeters}m.`);
    }
}
class Snake extends Animal { // 使用extends关键字继承
    constructor(name: string) { super(name); } // 在使用this之前，必须现使用super
    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);

二、公共，私有与受保护的修饰符

都过没有使用关键字，默认都是“public”

class Person {
    protected name: string; // protected表示受保护的，只可在本身和派生类中使用
    constructor(name: string) { this.name = name; }
}
class Employee extends Person {
    private department: string; // private表示私有，只在该类申明中可以使用
    constructor(name: string, department: string) {
        super(name)
        this.department = department;
    }
    public getElevatorPitch() { // public表示公共类，默认
        return `Hello, my name is ${this.name} and I work in ${this.department}.`;
    }
}
let howard = new Employee("Howard", "Sales");
console.log(howard.getElevatorPitch());
console.log(howard.name); // 错误

三、readonly 修饰符

只读属性必须在声明时或构造函数里被初始化。

class Octopus {
    readonly name: string;
    readonly numberOfLegs: number = 8;
    constructor (theName: string) {
        this.name = theName;
    }
      // constructor(private name: string) { } // 也可以使用参数属性来申明，参数属性通过给构造函数参数添加一个访问限定符来声明，比如private、public或protected
}
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、存取器

截取对对象成员的访问，一个拦截器

const fullNameMaxLength = 10;
class Employee {
    private _fullName: string;
    get fullName(): string { // getters，读取值的时候，会触发这个方法
        return this._fullName;
    }
    set fullName(newName: string) { // setters，设置某个值的时候，会触发这个方法
        if (newName && newName.length > fullNameMaxLength) {
            throw new Error("fullName has a max length of " + fullNameMaxLength);
        }
        this._fullName = newName;
    }
}
let employee = new Employee();
employee.fullName = "Bob Smith"; // 设置
if (employee.fullName) {
    alert(employee.fullName);
}

五、静态属性

存在于类本身上面而不是类的实例上，不需要实例话就可以访问的属性，使用static关键字

class Grid {
    static origin = {x: 0, y: 0}; // 定义静态属性
    calculateDistanceFromOrigin(point: {x: number; y: number;}) {
        let xDist = (point.x - Grid.origin.x); // 读取静态属性
        let yDist = (point.y - Grid.origin.y);
        return Math.sqrt(xDist * xDist + yDist * yDist) / this.scale;
    }
    constructor (public scale: number) { }
}
let grid1 = new Grid(1.0);  // 1x scale
let grid2 = new Grid(5.0);  // 5x scale
console.log(grid1.calculateDistanceFromOrigin({x: 10, y: 10}));
console.log(grid2.calculateDistanceFromOrigin({x: 10, y: 10}));

六、抽象类

抽象类做为其它派生类的基类使用，abstract 关键字是用于定义抽象类和在抽象类内部定义抽象方法。类似于类的接口

abstract class Department {
    constructor(public name: string) {
    }
    printName(): void {
        console.log('Department name: ' + this.name);
    }
    abstract printMeeting(): void; // 必须在派生类中实现
}
class AccountingDepartment extends Department {
    constructor() {
        super('Accounting and Auditing'); // 在派生类的构造函数中必须调用 super()
    }
    printMeeting(): void {
        console.log('The Accounting Department meets each Monday at 10am.');
    }
    generateReports(): void {
        console.log('Generating accounting reports...');
    }
}
let department: Department; // 允许创建一个对抽象类型的引用
department = new Department(); // 错误: 不能创建一个抽象类的实例
department = new AccountingDepartment(); // 允许对一个抽象子类进行实例化和赋值
department.printName();
department.printMeeting();
department.generateReports(); // 错误: 方法在声明的抽象类中不存在

七、高级技巧

类定义会创建两个东西：类的实例类型和一个构造函数

1，构造函数

class Greeter {
    static standardGreeting = "Hello, there"; // 申明静态属性
    greeting: string; // 申明公共属性
    greet() {
        if (this.greeting) {
            return "Hello, " + this.greeting;
        }
        else {
            return Greeter.standardGreeting;
        }
    }
}
let greeter1: Greeter; // 把类当类型使用
greeter1 = new Greeter();
console.log(greeter1.greet());
let greeterMaker: typeof Greeter = Greeter; // 申明的这个变量类型是Greeter，值也是Greeter
greeterMaker.standardGreeting = "Hey there!"; // 可以读取这个类的静态方法
let greeter2: Greeter = new greeterMaker();// 可以实例话刚才申明的类
console.log(greeter2.greet());

2，把类当做接口使用

class Point {
    x: number;
    y: number;
}
interface Point3d extends Point {
    z: number;
}
let point3d: Point3d = {x: 1, y: 2, z: 3};