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
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};