Thread: Java:Evaluation of Mathematical Expression only from left to right only.

I have written a Java program which evaluates a mathematical expression from left to right only.however im stuck up with the output.Im not getting the desired output.
Please Note: There is no precedence in operators(evaluation should be from LEFT->RIGHT.)

/*
 * Created on Jul 10, 2011
 *
 * To change the template for this generated file go to
 * Window>Preferences>Java>Code Generation>Code and Comments
 */
package com.comcast;
import java.util.*;
public class Evaluation
{
    private static final char[] validOperators = {'/','*','+','-'};
 
	private Evaluation()
	{
		 /* Using a private contructor to prevent instantiation
			 Using class as a simple static utility class
		 */
	}
 
	private static int evaluate(String leftSide, char oper, String rightSide)
	 throws IllegalArgumentException
	{
		System.out.println("Evaluating: " + leftSide +  " (" + oper + ") " + rightSide);
		int total = 0;
		int leftResult = 0;
		int rightResult = 0;
		String originalString =leftSide;
		int operatorLoc  = findOperatorLocation(leftSide);
		leftSide = leftSide.substring(0,operatorLoc);
		rightSide = originalString.substring(operatorLoc+1,operatorLoc+2);
		String remainingString = originalString.substring(operatorLoc+2,originalString.length());
 
 
		System.out.println("leftSide -->"+leftSide);
		System.out.println("rightSide -->"+rightSide);
		System.out.println("remainingString --->"+remainingString);
 
	 try{
			 leftResult = Integer.parseInt(leftSide);
		}catch(Exception e){
				throw new IllegalArgumentException("Invalid value found in portion of equation: "
				  + leftSide);
	    }
 
 
	 try{
			 rightResult = Integer.parseInt(rightSide);
	   }catch(Exception e){
				throw new IllegalArgumentException("Invalid value found in portion of equation: "
				  + rightSide);
	   }
 
 
		System.out.println("Getting result of: " + leftResult + " " + oper + " " + rightResult);
		switch(oper)
		{
			case '/':
			 total = leftResult / rightResult; break;
			case '*':
			 total = leftResult * rightResult; break;
			case '+':
			 total = leftResult + rightResult; break;
			case '-':
			 total = leftResult - rightResult; break;
			default:
			 throw new IllegalArgumentException("Unknown operator.");
		}
		System.out.println("Returning a result of: " + total);
		String totally = String.valueOf(total)+remainingString;
		return evaluate(totally,findCharacter(totally),remainingString);
	}
 
	private static int findOperatorLocation(String string)
		{
			int index = -1;			
				index = string.indexOf(string.substring(1,2));			    
				if(index >= 0){				
				 return index;
				}
			return index;
		}
 
	private static char findCharacter(String string){
 
		char c='\u0000';  
		int index = -1;			
						index = string.indexOf(string.substring(1,2));
						if(index >= 0){				
						 c = string.charAt(index);
						 return c;
						} 		 			 	
		 return c;	
	}
 
	public static int processEquation(String equation)
	  throws IllegalArgumentException
	{
		  return evaluate(equation,'+',"0");
	}
 
	public static void main(String[] args)
	{
		//String usage = "Usage: java MathParser equation\nWhere equation is a series"
		// + " of integers separated by valid operators (+,-,/,*)";
 
		//if(args.length < 1 || args[0].length() == 0)
		// System.out.println(usage);
		Scanner input = new Scanner(System.in); 
		System.out.print("Enter the equation to be evaluated ");
 
		String equation = (String)input.next();
			int result = Evaluation.processEquation(equation);
		 System.out.println("The result of your equation ("
			   + equation + ") is: " + result);
 
		//catch(IllegalArgumentException iae)
		//{
		//	System.out.println(iae.getMessage() + "\n" + usage);
		//}
	}
}

Expression Input:3+5*2-5 =>3+5*2-5 =>8*2-5 =>16-5 =>Expected Output :11

im getting as below output Enter the equation to be evaluated 3+5*2-5
Evaluating: 3+5*2-5 (+) 0
leftSide -->3
rightSide -->5
remainingString --->*2-5
Getting result of: 3 + 5
Returning a result of: 8
Evaluating: 8*2-5 ( * ) *2-5
leftSide -->8
rightSide -->2
remainingString --->-5
Getting result of: 8 * 2
Returning a result of: 16
Evaluating: 16-5 (6) -5
leftSide -->1
rightSide -->-
remainingString --->5
Exception in thread "main" java.lang.IllegalArgumentException: Invalid value found in portion of equation: -
at Evaluation.evaluate(Evaluation.java:49)
at Evaluation.evaluate(Evaluation.java:70)
at Evaluation.evaluate(Evaluation.java:70)
at Evaluation.processEquation(Evaluation.java:98)
at Evaluation.main(Evaluation.java:112)

Im unable to make my program generic for any equation entered.Help provided will be appreciated.Please note this is not a homework question.
Need help !!!!!Code fix required for the above program

You must have a logic error or a bad expression.
Have you tried more debugging aids by adding more printlns to show how the variables change?

The problem is in the method operatorLoc where im hardcoding the subString(1,2) to find location of operator,when i encounter 16-5,it returns a wrong location for operator.which is (6) instead of (-).

Need help in resolving this ? Please provide the bug fix for the same.

operatorLoc where im hardcoding the subString(1,2) to find location of operator,when i encounter 16-5,it returns a wrong location for operator.which is (6) instead of (-).

Can you explain what this code is supposed to do:

index = string.indexOf(string.substring(1,2));

Also what different values will it return?

Hi Junky,Can you provide the code fix for my code.??

Look at post#4 again. Can you describe what that code is supposed to do?
The way it is coded, it will always set index to 1. Unless the string is too short.