Simple factory model of Java design pattern

When writing a calculator program, you can separate the business logic from the display, and the business logic is encapsulated as a class (encapsulation); If you want to add a new operation, you can create a operation base class first, and then the various operations inherit from the Operation class and implement the GetResult () virtual function, Adding a new operation just needs to derive a new class that does not require previous operations to participate in the compilation. How do I get the calculator to know what kind of arithmetic I want to use? Separate classes should be considered to do the process of creating the instance, which is the factory. Create a Operationfactory class, pass in parameters, function createoperate can instantiate the appropriate object.

The Java code is as follows:

public class Operationfactory {public static abstract class Operation {private Double _numbera = 0;
  
  Private double _numberb = 0;
  Public double Get_numbera () {return _numbera;
  The public void Set_numbera (double _numbera) {This._numbera = _numbera;
  Public double Get_numberb () {return _numberb;
  The 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 ();
 }
}

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