TypeScript-Class
typescript之旅
1.TypeScript-Basic
2.TypeScript interface
3.Typescript-module(1)
4.TypeScript Modules(2)
5.Typescript tsconfig
6.TypeScript Functions
7.Typescript Class
Class
class Greeter {
greeting: string;
constructor(message: string) {
this.greeting = message;
}
greet() {
return "Hello, " + this.greeting;
}
}
let greeter = new Greeter("world");
对于这个demo的理解怎么说呢?
如果你是java或C#程序员,你应该这样理解:
public class Greeter{
public String greeting;
public Greeter(String message){
this.greeting = message;
}
public string greet(){
return "Hello, " + this.greeting;
}
}
如果你是javascript程序员,那你应该这样理解
function Greeter(message){
this.greeting = message;
}
Greeter.prototype.greet = function(){
return "Hello, " + this.greeting;
}
参数属性
对于上个例子,有一种简写方法
class Animal {
constructor(private name: string) { }
move(distanceInMeters: number) {
console.log(`${this.name} moved ${distanceInMeters}m.`);
}
}
仅在构造函数里使用private name: string参数来创建和初始化name成员。 我们把声明和赋值合并至一处。
参数属性通过给构造函数参数添加一个访问限定符来声明。 使用private限定一个参数属性会声明并初始化一个私有成员;对于public和protected来说也是一样。
继承
class Animal {
name:string;
constructor(theName: string) { this.name = theName; }
move(distanceInMeters: number = 0) {
console.log(`${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);
这个代码的理解呢?java程序员应该很好理解吧,子类重写了父类方法move,然后父类引用指向子类对象,多态实现了!
重点是javascript如何理解呢?
本质是javascript的原型继承,如果你想了解javascript继承高仿
OOP,我这里有一篇文章javascript继承
公共,私有与受保护的修饰符
想必是java同学前面一直有的疑问吧?
首先记住默认共有
第一个例子我可是全部加了public关键字的哦
理解private
class Animal {
private name: string;
constructor(theName: string) { this.name = theName; }
}
new Animal("Cat").name; // Error: 'name' is private;
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。例如:
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() {
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); // error
构造函数也可被标记为protected. 这就是说这个类不能在包含它的类之外实例外,但是可以被继承。比如,
class Person {
protected name: string;
protected constructor(theName: string) { this.name = theName; }
}
// Employee can extend 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"); // Error: The 'Person' constructor is protected
想什么,对抽象类
Get/Set
class Employee {
private _fullName: string;
get fullName(): string {
return this._fullName;
}
set fullName(newName: string) {
if (passcode && passcode == "secret passcode") {
this._fullName = newName;
}
else {
console.log("Error: Unauthorized update of employee!");
}
}
}
let employee = new Employee();
employee.fullName = "Bob Smith";
if (employee.fullName) {
alert(employee.fullName);
}
和C#很像
静态属性
使用很简单的,属性前加static关键字
class Grid {
static origin = {x: 0, y: 0};
calculateDistanceFromOrigin(point: {x: number; y: number;}) {
let xDist = (point.x - Grid.origin.x);
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}));
console.log(Grid.origin);
抽象类
abstract class Animal {
abstract makeSound(): void;
move(): void {
console.log('roaming the earch...');
}
}
高级技巧
class Greeter {
greeting: string;
constructor(message: string) {
this.greeting = message;
}
greet() {
return "Hello, " + this.greeting;
}
}
var greeter: Greeter;
greeter = new Greeter("world");
alert(greeter.greet());
greeter的类型是Greeter, Greeter的类型是typeof Greeter
class Greeter {
static standardGreeting = "Hello, there";
greeting: string;
greet() {
if (this.greeting) {
return "Hello, " + this.greeting;
}
else {
return Greeter.standardGreeting;
}
}
}
var greeter1: Greeter;
greeter1 = new Greeter();
alert(greeter1.greet());
var greeterMaker: typeof Greeter = Greeter;
greeterMaker.standardGreeting = "Hey there!";
var greeter2:Greeter = new greeterMaker();
alert(greeter2.greet());
这个语法不常用,据我所知只在动态加载中有用
抽象方法的语法与接口方法相似:定义方法签名不包含方法体
区别:抽象类:抽象方法必须使用abstract关键字并且可以包含访问符