2.定義圖形類Shape，該類中有得到面積的方法getArea()；定義長方形類Rect，該類是Shape的子類，類中有矩形長和寬的變量double a,double b，設置長和寬的方法setWid

// 圖形類Shape package d922B;html public class Shape { double getArea(ShapePara x){ return x.getArea(); } double getArea(Rect y) { return y.getA()*y.getB(); }markdown } //矩形類 package d922B;post public cl

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