Use math operators on generic variables in a generic Java class

问题

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.

回答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());      
}

回答2:

Java does not allow operators to be called on classes (so no +, -, *, /) you have to do the math as a primitive (I was going to show the code... but jjnguy beat me to it :-).

来源：https://stackoverflow.com/questions/4028358/use-math-operators-on-generic-variables-in-a-generic-java-class

标签

java

generics

math