java 一个泛型类的类型变量所对应的实际类型是两个泛型类，怎么弄？

package genercityArea;
public interface Area<T>{ public double area();}
package genercityArea;
public class Circular<T extends Number> implements Area{private T a;public Circular(T a){this.a=a;}public double area( ) {
double s=a.doubleValue();
return s*s*Math.PI;}} package genercityArea;
public class Square<T extends Number> implements Area{private T a;public Square (T a){this.a=a;}public double area() {
double s=a.doubleValue();
return s*s;}
}
package genercityArea;
public class GenArea <T extends Area>{Area a;public GenArea (Area a){this.a=a;}
public void printArea(){java.text.DecimalFormat df=new java.text.DecimalFormat("#0.00");System.out.println("面积是： "+df.format(a.area( ))); }
} package genercityArea;
import java.util.Scanner;
public class Textmian {public static void main(String[] args){System.out.print("请输入圆形的半径： ");Scanner scanner = new Scanner(System.in);double t= scanner.nextDouble();
Circular<Double> a= new Circular<Double> (t);GenArea<Area<Double>> g=new GenArea<Area<Double>>(a);g.printArea();System.out.print("请输入正方形边长： ");int w= scanner.nextInt();Square<Integer> b= new Square<Integer> (w);GenArea<Square<Integer>> h=new GenArea<Square<Integer>>(b);h.printArea();}
}

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