การนำไปใช้งาน

สรุปแผน

โค้ด: คลาสฐานและ Circle

public class Main {
  // Base class with a tiny print helper
  static abstract class Shape {
    abstract double area();
    abstract double perimeter();
    String info() {
      return String.format("area=%.2f, per=%.2f", area(), perimeter());
    }
  }
  static class Circle extends Shape {
    double radius;
    Circle(double r) {
      // simple guard to avoid negative sizes for beginners
      radius = (r < 0) ? 0 : r;
    }
    double area() { return Math.PI * radius * radius; }
    double perimeter() { return 2 * Math.PI * radius; }
    public String toString() { return "Circle " + info(); }
  }

  public static void main(String[] args) {
    Shape s = new Circle(2.5);
    System.out.println(s); // prints Circle area/perimeter
  }
}

ตัวสร้างและการป้องกันค่า

โค้ด: เพิ่ม Rectangle

public class Main {
  static abstract class Shape {
    abstract double area();
    abstract double perimeter();
    String info() { return String.format("area=%.2f, per=%.2f", area(), perimeter()); }
  }
  static class Circle extends Shape {
    double radius;
    Circle(double r) { radius = (r < 0) ? 0 : r; }
    double area() { return Math.PI * radius * radius; }
    double perimeter() { return 2 * Math.PI * radius; }
    public String toString() { return "Circle " + info(); }
  }
  static class Rectangle extends Shape {
    double w, h;
    Rectangle(double w, double h) {
      this.w = (w < 0) ? 0 : w;
      this.h = (h < 0) ? 0 : h;
    }
    double area() { return w * h; }
    double perimeter() { return 2 * (w + h); }
    public String toString() { return "Rectangle " + info(); }
  }

  public static void main(String[] args) {
    Shape a = new Circle(3.0);
    Shape b = new Rectangle(4.0, 2.0);
    System.out.println(a);
    System.out.println(b);
  }
}

รายการและการพิมพ์

โค้ด: รายงานขนาดเล็ก

public class Main {
  static abstract class Shape {
    abstract double area();
    abstract double perimeter();
    String label() { return getClass().getSimpleName(); }
    String info() { return String.format("area=%.2f, per=%.2f", area(), perimeter()); }
  }
  static class Circle extends Shape {
    double radius;
    Circle(double r) { radius = (r < 0) ? 0 : r; }
    double area() { return Math.PI * radius * radius; }
    double perimeter() { return 2 * Math.PI * radius; }
  }
  static class Rectangle extends Shape {
    double w, h;
    Rectangle(double w, double h) { this.w = (w < 0) ? 0 : w; this.h = (h < 0) ? 0 : h; }
    double area() { return w * h; }
    double perimeter() { return 2 * (w + h); }
  }

  public static void main(String[] args) {
    Shape[] shapes = { new Circle(1.2), new Rectangle(2.0, 3.0), new Circle(0.5) };
    for (int i = 0; i < shapes.length; i = i + 1) {
      Shape s = shapes[i];
      System.out.println(s.label() + " -> " + s.info());
    }
  }
}

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