Java calling methods from other methods

Question

Is there a way I can pass one of the 3 functions fun1 to fun3 as argument to eval and then evaluate it? The code:

public class Pruebas {
    public static double fun1(double x){
        return x*1;
    }
    public static double fun2(double x){
        return x*2;
    }
    public static double fun3(double x){
        return x*3;
    }
    public static double eval(funx,double x0){
       /* funx at this point i expect it to be fun1, fun2 or fun3 */
       double f=funx(x0);
       return f;
    }
}

Check out reflection: http://stackoverflow.com/questions/37628/what-is-reflection-and-why-is-it-useful — Marv, Mar 14 '16 at 16:22
There are several means. Which to use depends on the situation. What are you trying to achieve? — Raedwald, Mar 14 '16 at 16:24
Depending on what you want to do, the [Strategy and Template Method design patterns](http://stackoverflow.com/questions/669271/what-is-the-difference-between-the-template-method-and-the-strategy-patterns) can be useful for this. — Raedwald, Mar 14 '16 at 16:26
Hi thanks for replying, I simplified the problem, but what I´m doing is a thermodinamics program that uses a lot of mathematics specificly numerical methods that require me to evaluate a lot of functions a lot of times with different input arguments each time. — Richard, Mar 14 '16 at 16:42
Oh, wait. In your sample code, all 3 of your `funx()` methods take a single argument of type `double`. Is that the case in your real code? Do all of the methods that you want to do this with take one argument of type `double` (or at least of the same type)? — Erick G. Hagstrom, Mar 14 '16 at 16:53
Yes they all take double arguments, some of them take more than one but I can change that if necesary. — Richard, Mar 14 '16 at 17:19

score 3 · Accepted Answer · answered Mar 14 '16 at 16:27

You can use Method References if you can afford Java 8

package javaapplication4;

import java.util.function.Function;

public class JavaApplication4 {

    public static class Pruebas 
    {
       public static double fun1(double x)
       {
           return x*1;
       }

       public static double fun2(double x){
           return x*2;
       }
       public static double fun3(double x){
           return x*3;
       }

       public static double eval(Function<Double, Double> fun,double x0)
       {
          double f=fun.apply(x0);
          return f;
       }
    }


    public static void main(String[] args) 
    {
        System.out.println(Pruebas.eval(Pruebas::fun3, 5));
    }

}

William B. · Answer 2 · 2016-03-14T16:33:29.157

usually, the way to do this would be to create an interface and then have 3 implementing classes. For example,

public interface FuncInterface
{
    public double func(double x);
}
public class Pruebas {
    public class Func1 implements FuncInterface {
        public static double func(double x){
           return x*1;
        }
    }
    public class Func2 implements FuncInterface {
        public static double func(double x){
           return x*2;
        }
    }
    public class Func3 implements FuncInterface {
        public static double func(double x){
           return x*3;
        }
    }
    public static double eval(FuncInterface funcI,double x0){
       /* funx at this point i expect it to be fun1, fun2 or fun3 */
       double f=funcI.func(x0);
       return f;
    }
}

Java calling methods from other methods

2 Answers2