对通用Java类中的泛型变量使用数学运算符

Question

I'm trying to write some code that will allow me to perform basic math operations on a "T extends Number" object instance. It needs to be able to handle any number type that is a subclass of Number .
I know some of the types under Number have .add() methods built in, and some even have .multiply() methods. I need to be able to multiply two generic variables of any possible type. I've searched and searched and haven't been able to come up with a clear answer of any kind.

public class Circle<T extends Number> {

private T center;
private T radius;
private T area;

// constructor and other various mutator methods here....

/**
  The getArea method returns a Circle
  object's area.
  @return The product of Pi time Radius squared.
*/
public Number getArea() {
    return  3.14 * (circle.getRadius()) * (circle.getRadius());      
}  

Any help would be much appreciated. Generics are the most difficult thing I've encountered in learning Java. I don't mind doing the leg work because I learn better that way, so even a strong point in the right direction would be very helpful.

Answer 1

What you will need to do is use the double value of the Number . However, this means that you cannot return the Number type.

public double getArea()
{
    return  3.14 * 
            (circle.getRadius().doubleValue()) * 
            (circle.getRadius().doubleValue());      
}  

Answer 2

Java不允许在类上调用运算符（所以没有+， - ，*，/）你必须把数学作为一个原语（我打算显示代码......但是jjnguy打败了我:-) 。

Answer 3

你应该查看http://code.google.com/p/generic-java-math/ ，它解决了java中泛型算法的问题，甚至可能有你想要的几何函数。