public class OperationFactory {
 public static abstract class Operation
 {  
  private double _numberA = 0;
  private double _numberB = 0;
  
  public double get_numberA() {
   return _numberA;
  }

  public void set_numberA(double _numberA) {
   this._numberA = _numberA;
  }

  public double get_numberB() {
   return _numberB;
  }

  public void set_numberB(double _numberB) {
   this._numberB = _numberB;
  }
  
  abstract double GetResult();
  // TODO Auto-generated constructor stub
 }
 
 public static class OperationAdd extends Operation
 {
  double GetResult() 
  {
   double result = get_numberA() + get_numberB();
   return result;
  }  
 }
 
 public static class OperationSub extends Operation
 {
  double GetResult() {
   double result = get_numberA() - get_numberB();
   return result; 
  }
 }
 
 
 public static Operation createOperate(String operate){
  Operation oper = null;
  if (operate.equals("+")) {
   oper = new OperationAdd();
  }
  else if (operate.equals("-")) {
   oper = new OperationSub();
  }

  return oper;
 }

 public static void main(String[] args) {
  Operation oper;
  oper = OperationFactory.createOperate("+");
  oper.set_numberA(1);
  oper.set_numberB(2);
  double result = oper.GetResult();
 }
}