package com.mycompany.test;

public class Calculator {

  public static void main(String[] args){
    int a=4;
    int b=2;
    System.out.println( sum(a,b));
  }

  private static int sum(int a, int b){
    return a+b;
  }
  private static int minus(int a, int b){
    return a-b;
  }
}

package com.mycompany.test;

public class Calculator {

  public static void main(String[] args){
    int a=4;
    int b=2;
    System.out.println( sum(a,b));
  }

  private static int sum(int a, int b){
    return a+b;
  }
  private static int minus(int a, int b){
    return a-b;
  }

  public static int minus(int a, int b, Object GPU){
    int result = 0;
    if(GPU == null){
      result = a-b;
    }
    else{
      result = a-b;
    }
    return result;
  }
}

Add minus() for GPU