class Animal {
    name: string;

    constructor(name: string) {
        this.name = name;
    }

    speak(): void {
        console.log(this.name + " 发出声音");
    }
}

class Dog extends Animal {
    breed: string;

    constructor(name: string, breed: string) {
        super(name);  // 调用父类构造函数
        this.breed = breed;
    }

    speak(): void {
        console.log(this.name + " 汪汪汪!");
    }
}

var dog = new Dog("旺财", "金毛");
dog.speak();

class Shape {
    color: string;

    constructor(color: string) {
        this.color = color;
    }

    describe(): string {
        return "这是一个 " + this.color + " 的图形";
    }
}

class Circle extends Shape {
    radius: number;

    constructor(color: string, radius: number) {
        super(color);
        this.radius = radius;
    }

    // 重写父类方法
    describe(): string {
        // 调用父类方法并扩展
        return super.describe() + "，半径是 " + this.radius;
    }

    area(): number {
        return Math.PI * this.radius * this.radius;
    }
}

var circle = new Circle("红色", 5);
console.log(circle.describe());
console.log("面积: " + circle.area().toFixed(2));

class Animal {
    name: string;
    constructor(name: string) { this.name = name; }
    speak(): void {
        console.log(this.name + " 发出声音");
    }
}

class Cat extends Animal {
    speak(): void {
        console.log(this.name + " 喵喵喵!");
    }
}

class Dog extends Animal {
    speak(): void {
        console.log(this.name + " 汪汪汪!");
    }
}

// 多态：数组中存储不同子类的实例
var animals: Animal[] = [
    new Cat("小白"),
    new Dog("旺财"),
    new Animal("动物")
];

// 调用同一方法，不同子类有不同实现
for (var _i = 0, animals_1 = animals; _i < animals_1.length; _i++) {
    var animal = animals_1[_i];
    animal.speak();
}

class Rectangle {
    width: number;
    height: number;
    constructor(width: number, height: number) {
        this.width = width;
        this.height = height;
    }
    area(): number {
        return this.width * this.height;
    }
}

class Circle {
    radius: number;
    constructor(radius: number) {
        this.radius = radius;
    }
    area(): number {
        return Math.PI * this.radius ** 2;
    }
}

var shapes = [new Rectangle(4, 5), new Circle(3)];

for (var _i = 0, shapes_1 = shapes; _i < shapes_1.length; _i++) {
    var shape = shapes_1[_i];
    if (shape instanceof Rectangle) {
        console.log("矩形面积: " + shape.area());
    } else if (shape instanceof Circle) {
        console.log("圆形面积: " + shape.area().toFixed(2));
    }
}

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 introduce(): string {
        // 可以访问 protected 成员
        return "我是 " + this.name + "，在 " + this.department + " 工作";
    }
}

var emp = new Employee("Alice", "技术部");
console.log(emp.introduce());

// console.log(emp.name); // 错误：protected 外部不可访问