使用typescript 1、 创建一个接口Shape，接口中定义两个方法getArea()与getLength()分别用于求图形面积与周长。定义两个图形类Circle（属性：radius 半径）与Square（属性：width length）实现该接口，在构造方法中分别初始化半径与长宽，调用getArea()与getLength()计算图形面积与周长。

可以按照以下代码实现：

interface Shape {
  getArea(): number;
  getLength(): number;
}

class Circle implements Shape {
  radius: number;

  constructor(radius: number) {
    this.radius = radius;
  }

  getArea(): number {
    return Math.PI * this.radius ** 2;
  }

  getLength(): number {
    return 2 * Math.PI * this.radius;
  }
}

class Square implements Shape {
  width: number;
  length: number;

  constructor(width: number, length: number) {
    this.width = width;
    this.length = length;
  }

  getArea(): number {
    return this.width * this.length;
  }

  getLength(): number {
    return 2 * (this.width + this.length);
  }
}

可以这样使用：

const circle = new Circle(5);
console.log(circle.getArea()); // 78.53981633974483
console.log(circle.getLength()); // 31.41592653589793

const square = new Square(3, 4);
console.log(square.getArea()); // 12
console.log(square.getLength()); // 14