presenting a simple calculator, needs help urgently

[greeninho]

Happy sunday to all. I have been to write programs on simple arithmetic operations but i encountered a problem trying to put the whole individual operation as one program. What i mean is that want a situation where if (an assumption) both an additional and a subtraction program are written as one program, whereby one is given an option of like 'click here to add or subtract' something of that kind. I need help on how to go about it, hope my thread is clear and understandable?

[Fou-Lu]

Since we have no idea what you have done, I can only suggest routes in which you can decouple the arithmetic control from the calculator itself. For that, a simple interface, a calculator, and each class written individual would work fine. This one I wrote a calculator with a hashtable to register ops to the calculator. Wrote a simple main test without any error checking in it, and it works fine:

package calc;

public interface IOperation
{	
	public void registerOperation(Calculator calc);
	public double calculate(double lhs, double rhs);
}

// Add
package calc;

public class Add implements IOperation
{

	public Add(Calculator calc)
	{
		this.registerOperation(calc);
	}

	@Override
	public void registerOperation(Calculator calc)
	{		
		calc.registerOperation("+", this);
	}

	@Override
	public double calculate(double lhs, double rhs)
	{
		return lhs + rhs;
	}

}

// Calculator
package calc;

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Scanner;

public class Calculator
{
	private Hashtable<String, IOperation> htOps = new Hashtable<String, IOperation>();
	public void registerOperation(String sOp, IOperation iOp)
	{
		this.htOps.put(sOp, iOp);
	}
	
	public IOperation getOperation(String sOp)
	{
		return this.htOps.get(sOp);
	}
	
	public double calculate(IOperation op, double lhs, double rhs)
	{
		return op.calculate(lhs, rhs);
	}
	
	public static void main(String... argv)
	{		
		Scanner s = new Scanner(System.in);
		double lhs, rhs;
		String sOp;
		StringBuffer opList = new StringBuffer();
		int i = 0;
	
		Calculator c = new Calculator();
		new Add(c);
		
		Enumeration<String> e = c.htOps.keys();
		while (e.hasMoreElements())
		{
			if (i++ > 0)
			{
				opList.append(", ");
			}
			opList.append(e.nextElement());
		}

		System.out.print("Enter lhs: ");
		lhs = s.nextDouble();
		s.nextLine();
		System.out.print("Enter ops (from list: " + opList + "):");
		sOp = s.nextLine();
		
		System.out.print("Enter rhs: ");
		rhs = s.nextDouble();
		s.nextLine();
		System.out.println(c.calculate(c.getOperation(sOp), lhs, rhs));
		
	}
}

I used the console, but a gui would work fine as well.
Registering on the calculator is optional. The classes are easier written without the registration at all, but I liked the idea of giving a list of what the calculator could do.