經濟部國營事業聯招
資訊類 專業科目B 歷屆全真詳解教材

abstract class Shape {
public abstract double getArea(); // 抽象方法定義多型介面
}
class Circle extends Shape {
private double r;
public Circle(double r) { this.r = r; }
@Override public double getArea() { return Math.PI * r * r; }
}
class Rectangle extends Shape {
private double w, h;
public Rectangle(double w, double h) { this.w = w; this.h = h; }
@Override public double getArea() { return w * h; }
}
// 執行期動態繫結示範：
Shape s1 = new Circle(5.0);
Shape s2 = new Rectangle(4.0, 6.0);
System.out.println(s1.getArea()); // 自動呼叫 Circle 實作
System.out.println(s2.getArea()); // 自動呼叫 Rectangle 實作