類常用的語法：

1. extends與super
2. private姻僧、public、protected、readonly
3. get、set
4. 抽象類

1.extends與super

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);
    }
}
let sam = new Snake("Sammy the Python");

2. private耐薯、public、protected丝里、readonly

class Animal {
    public name: string; // 都可以訪問
    private age: number;// 類的內(nèi)部可以訪問
    protected color: string; // protected的屬性可柿，可以在派生類中訪問
    readonly other: string; //只讀屬性
}

1. 類的屬性默認是public。
2. private屬性不能被聲明的類訪問丙者。
3. protected不能類外訪問該屬性，但可以通過實例方法訪問到該屬性营密。

3. get set(通過get械媒、set函數(shù)聲明該屬性)

let passcode = "secret passcode";
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);
}

4. 抽象類

abstract class Department {
    constructor(public name: string) {
    }
    printName(): void {
        console.log('Department name: ' + this.name);
    }
    abstract printMeeting(): void; // 必須在派生類中實現(xiàn)
}

class AccountingDepartment extends Department {
    constructor() {
        super('Accounting and Auditing'); // 在派生類的構(gòu)造函數(shù)中必須調(diào)用 super()
    }
    printMeeting(): void {
        console.log('The Accounting Department meets each Monday at 10am.');
    }
    generateReports(): void {
        console.log('Generating accounting reports...');
    }
}

let department: Department; // 允許創(chuàng)建一個對抽象類型的引用
department = new Department(); // 錯誤: 不能創(chuàng)建一個抽象類的實例
department = new AccountingDepartment(); // 允許對一個抽象子類進行實例化和賦值
department.printName();
department.printMeeting();
department.generateReports(); // 錯誤: 方法在聲明的抽象類中不存在