java 安卓重写子类中的函数

Question

我创建了一个类图，然后从中创建了两个子类。Figure super类有一个名为are（）的方法。这是全班的

public class Figure
{
  public double a, b;
  public Figure(double a,double b) {
    this.a = a; 
    this.b = b;
  }

  public double are() {
    return 0;
  }
}

public class Rectangle extends Figure
{
  Rectangle(double a, double b) {
    super(a,b);
  }

  double area (){
    return this.a*this.b;
  }
}

class Triangle extends Figure
{
  Triangle(double a, double b) {
    super(a,b);
  }
  // override area for right triangle
  double area () {
    return a * b / 2;
  }
}

为了便于打印输出，我制作了

public  void toastM(String str) { 
  Toast.makeText(getApplicationContext(), str, Toast.LENGTH_SHORT).show();
}

现在我使用这个代码

 Figure f = new Figure(10, 10);
 Rectangle r = new Rectangle(9, 5);
 Triangle t = new Triangle(10, 8);

 Figure figref;
 figref = r;
 toastM("are.....   " + figref.are());
 figref = t;
 toastM("are.....   " + figref.are());
 figref = f;
 toastM("are.....   " + figref.are());

预期值为45 40 0 但是它来了

Answer 1

父类有一个名为

double are()

儿童班

double area()

所以它没有被覆盖

Answer 2

在Rectangle和Triangle中重写的函数称为area，而不是像Figure类中那样are

Answer 3

调用的是超类Figure的are（）函数，而不是子类的area（）函数