พฤติกรรมแบบพหุรูปแบบ

ภาพรวม

รายการตรวจสอบส่วนติดต่อพื้นฐาน

โค้ด: การพิมพ์แบบเดียวกัน

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 r; Circle(double r) { this.r = (r < 0) ? 0 : r; }
    double area() { return Math.PI * r * r; }
    double perimeter() { return 2 * Math.PI * r; }
  }
  static class Rectangle extends Shape {
    double w, h; Rectangle(double w, double h) { this.w = Math.max(0, w); this.h = Math.max(0, h); }
    double area() { return w * h; }
    double perimeter() { return 2 * (w + h); }
  }
  public static void main(String[] args) {
    Shape[] list = { new Circle(2.0), new Rectangle(3.0, 4.0), new Circle(1.0) };
    for (int i = 0; i < list.length; i = i + 1) {
      Shape s = list[i];
      System.out.println(s.label() + " -> " + s.info());
    }
  }
}

แนวคิดการเรียงลำดับตาม area

โค้ด: เรียงลำดับตาม area

public class Main {
  static abstract class Shape { abstract double area(); abstract double perimeter(); String label(){ return getClass().getSimpleName(); } }
  static class Circle extends Shape { double r; Circle(double r){ this.r = Math.max(0, r);} double area(){return Math.PI*r*r;} double perimeter(){return 2*Math.PI*r;} }
  static class Rectangle extends Shape { double w,h; Rectangle(double w,double h){ this.w=Math.max(0,w); this.h=Math.max(0,h);} double area(){return w*h;} double perimeter(){return 2*(w+h);} }

  // Very small bubble sort for beginners (ascending by area)
  static void sortByArea(Shape[] arr){
    for(int pass=0; pass<arr.length-1; pass=pass+1){
      for(int i=0; i<arr.length-1; i=i+1){
        if(arr[i].area() > arr[i+1].area()){
          Shape tmp = arr[i]; arr[i] = arr[i+1]; arr[i+1] = tmp;
        }
      }
    }
  }

  public static void main(String[] args) {
    Shape[] a = { new Rectangle(3,4), new Circle(2), new Circle(1) };
    sortByArea(a);
    for(int i=0;i<a.length;i=i+1){
      System.out.println(a[i].label() + " area=" + String.format("%.2f", a[i].area()));
    }
  }
}

โค้ด: ผลรวม area

public class Main {
  static abstract class Shape { abstract double area(); abstract double perimeter(); }
  static class Circle extends Shape { double r; Circle(double r){ this.r=Math.max(0,r);} double area(){return Math.PI*r*r;} double perimeter(){return 2*Math.PI*r;} }
  static class Rectangle extends Shape { double w,h; Rectangle(double w,double h){ this.w=Math.max(0,w); this.h=Math.max(0,h);} double area(){return w*h;} double perimeter(){return 2*(w+h);} }

  static double totalArea(Shape[] arr){
    double sum = 0.0;
    for(int i=0;i<arr.length;i=i+1){
      sum = sum + arr[i].area(); // polymorphic call
    }
    return sum;
  }

  public static void main(String[] args) {
    Shape[] list = { new Circle(1), new Rectangle(2,3), new Circle(0.5) };
    System.out.println("Total area = " + String.format("%.2f", totalArea(list)));
  }
}

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