android - better structuring the Java code -

i have written piece of code assignment , want well-factored. basically, part of simple old-school calculator perform addition, subtraction, multiplication, division (when performing division, reminder should shown). required have separate classes each operation (addition, subtraction, multiplication, division have introduced 1 more - reminder). have advice or see gaps in understanding of concept of java generics?

public class logic         implements logicinterface {      private final int addition = 1;     private final int subtraction = 2;     private final int multiplication = 3;     private final int division = 4;      /**      * reference activity output.      */     protected activityinterface mout;      /**      * constructor initializes field.      */     public logic(activityinterface out){         mout = out;     }      /**      * perform @a operation on @a argumentone , @a argumenttwo.      */     public void process(int argumentone,                         int argumenttwo,                         int operation){          operationsinterface operationsinterface =null;          if(operation==addition)         {             operationsinterface = new add();         }         else if(operation==subtraction)         {             operationsinterface = new subtract();         }         else if(operation==multiplication)         {             operationsinterface = new multiply();         }         else         {             operationsinterface = new divide();         }      if(argumenttwo==0 && operation == division) {         mout.print("you cannot divide zero!");     }     else {         try {             //get result             int result = operationsinterface.process(argumentone, argumenttwo);             mout.print(string.valueof(result));              //add reminder output in case performing division             if (operation == division) {                 operationsinterface = new reminder();                 mout.print(result + " r: " + string.valueof(operationsinterface.process(argumentone, argumenttwo)));             }         }         catch (exception exception)         {             mout.print("something went wrong!");         }     }      } } 

i don't see has generics.

as code review point of view:

1. you should ask how easy change code when need extend functionality. in case, suppose want add operator. need add constant , add if/else case, , maybe other logic. suggest have map operator constants operating classes, or use enum that; need initialize once , save if/else cases.
2. consider having different add classes, 1 simple addition, , prints out something. if want exchange them, need change new add() part, cannot have 2 calculators, 1 simple add , extended one. therefore, practice use new in kind of factory method can overridden, e.g. protected operationinterface createadd() {return new add();}. can subclass calculator , override createadd(). same holds other operators, of course.
3. your operationinterface seems return int. not think works division. should @ least double.
4. i see reminder subclass of divide. @ least logic related division operations , should therefore located in divide class or subclass of it.