Simple Calculator

[Narendra kadimetla]

I am new to JAVA.I was asked to build a simple Add class and i did it this way..

public class addTest {
public int num1,num2,num3a;
public int addition(){
num1=30;num2=20;
        num3a=num1+num2;//used num3a for add,num3b for subtraction and so on..
        System.out.println(num3a);
  return(num3a);
                      }
                     }
 class add{
public static void main(String args[]){
addTest a=new addTest();
a.addition();
                                      }
 }

He then asked me to do Subtraction,Multiplication and Divison.I did them.
Now he wants me build a simple calculator using all these classes.
I am not getting anything...please help me...

[Greg Stevens]

What would the interface for the Add class be? How would you use an object of type Add?

[Devaka Cooray]

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[Campbell Ritchie]

You need to pass values to the add method, and that returns a result.

Are you sure you should have an Add class, rather than an Arithmetic class with a (static) add method?

[Matt Cartwright]

Campbell Ritchie wrote:You need to pass values to the add method, and that returns a result.

Are you sure you should have an Add class, rather than an Arithmetic class with a (static) add method?

This is definitely the way to go for all of your supported calculator operations.

Reorganizing the stack from the user input can be quite tricky though when using
infix notation. It might be a lot easier to enhance functionality step by step using
Reverse Polish Notation (RPN) internally.
You might wanna have a look here.

Good luck and please keep us posted
Matt

[Campbell Ritchie]

Is reverse Polish notation the same as postfix notation? Agree it is better, but it requires parsing skills, so it may be difficult to implement.

[Matt Cartwright]

Campbell Ritchie wrote:Is reverse Polish notation the same as postfix notation? Agree it is better, but it requires parsing skills, so it may be difficult to implement.

that's affirmative.

Postfix notation is just another name for RPN.

Regarding the parsing:

from my point of view it is much more difficult to
parse the entire infix statement than just stack
RPN instructions.

Just an opinion.

Matt

[Campbell Ritchie]

Agree it is much easier to put postfix/reverse Polish onto a stack, which I am doing myself in FORTH, but it does mean learning notation like 1 2 3 * + instead of 1 + 2 * 3. When I said "parsing skills" I thought Narendra kadimetla wanted to start with an infix expression (eg 1 + 2 * 3) and evaluate that correctly. When you said

quite tricky though when using infix notation

you must have been thinking on the same lines.