Factory Method

Question:Based on the previous article,what could you do if we must add an extra  function? For example,we need to numberA to the numberB;

Analysis:

we must update the class of 'Factroy' and continue to add another case in the expression  of 'switch - case' if we code based on ‘Simple Factory', and at the same time, we also must add a subclass to extend the class of Operation.Actually it does not accord with the principle of 'open - close' which means code is open for adding but closed for update. So in this example, we will introduce the pattern of 'Factory Method' as following.

What's Factory Method?

Here has an interface of Factory which can let its subclass to intantiate the object respectively according with the need of Client.

public class Operation {
 
 public double numberA = 0.0;
 
 public double numberB = 0.0;
 
 public double getResult(){
  
  double result = 0.0;
  
  return result;
 }
}

public interface IFactory {    

   public Operation getOperation();

}

public class AddFactory implements IFactory{

 @Override  public Operation getOperation() {     

      return new Add();

    }

}

public class Add extends Operation {  

   @Override  

  public double getResult() {

  double result = 0.0;  

  result = numberA + numberB;   

  return result;  

   }

}

Finally

Client:

public class Test {
 public static void main(String[] args) {
  IFactory add = new AddFactory();
  Operation oper = add.getOperation();
  oper.numberA = 22;
  oper.numberB = 11;
  double result = oper.getResult();
  System.out.println(result);
 }
}

In the Client,we still need to update the Client when the requirement is changed.