Help With Expression Solver

[bumwipe]

I am trying to create a program that takes string expressions and solves them mathematically (i.e. string "5 + 4 * 2" will evaluate as 13). i have this much of the program made, but I am not sure why it is not working. it keeps telling me there is a "Number Format Exception"

Please help!

import java.util.ArrayList;
import java.util.Scanner;
import static java.lang.Integer.*;
import static java.lang.System.*;
import java.lang.*;
 
class ExpSolver
{
    private ArrayList<String> list;
    private String expression;
    private String trimmedExp;
    private String evaluated;
    private int eval;
 
    public ExpSolver(String s)
    {
        list=new ArrayList<String>();
        expression=s;
        trimmedExp=s.trim();
        for (int x=0; x<trimmedExp.length(); x++)
        {
            list.add(""+trimmedExp.charAt(x));
        }
    }
 
    public void setExpression(String s)
    {
        expression=s;
        trimmedExp=s.trim();
        list.clear();
        for (int x=0; x<trimmedExp.length(); x++)
        {
            list.add(""+trimmedExp.charAt(x));
        }        
    }
 
    public void solveExpression()
    {
        eval=0;
        for (int x=0; x<list.size(); x++)
        {
            if (list.get(x).equals("*")||list.get(x).equals("/"))
            {
                if (list.get(x).equals("*"))
                {
                    list.set(x-1, String.valueOf(Integer.parseInt(list.get(x-1))*Integer.parseInt(list.get(x+1))));
                    list.remove(x+1);
                    list.remove(x);
 
                }
 
                else if(list.get(x).equals("/"))
                {
                    list.set(x-1, String.valueOf(Integer.parseInt(list.get(x-1))/Integer.parseInt(list.get(x+1))));
                    list.remove(x+1);
                    list.remove(x);
 
                }
            }
 
        }
 
        for (int x=0; x<list.size(); x++)
        {
            if (list.get(x).equals("-"))
            {
                list.set(x-1, String.valueOf(Integer.parseInt(list.get(x-1))-Integer.parseInt(list.get(x+1))));
                list.remove(x);
                list.remove(x+1);
            }
 
            else if (list.get(x).equals("+"))
            {
                list.remove(x);
            }
        }
        for (int x=0; x<list.size(); x++)
        {
            if (list.get(x).equals(" "))
            {
                list.remove(x);
            }
 
            list.set(x, list.get(x).trim());
        }
 
        for (int x=0; x<list.size(); x++)
        {
            eval+=Integer.parseInt(list.get(x));            
        }
 
        evaluated=String.valueOf(eval);
 
 
    }
 
    public String toString( )
    {
        return evaluated;
    }
}
 
public class Lab04b
{
    public static void main( String args[] )
    {
        ExpSolver test = new ExpSolver("3 + 5");
        test.solveExpression();
        out.println(test.toString());
 
        test.setExpression("3 * 5");
        test.solveExpression();
        out.println(test);
 
        test.setExpression("3 - 5");
        test.solveExpression();
        out.println(test);
 
        test.setExpression("3 / 5");
        test.solveExpression();
       out.println(test);
 
       test.setExpression("5 * 5 + 2 / 2 - 8 + 5 * 5 - 2");
        test.solveExpression();
        out.println(test);
    }
}
 
 

[r035198x]

I am trying to create a program that takes string expressions and solves them mathematically (i.e. string "5 + 4 * 2" will evaluate as 13). i have this much of the program made, but I am not sure why it is not working. it keeps telling me there is a "Number Format Exception"

Please help!

import java.util.ArrayList;
import java.util.Scanner;
import static java.lang.Integer.*;
import static java.lang.System.*;
import java.lang.*;
 
class ExpSolver
{
    private ArrayList<String> list;
    private String expression;
    private String trimmedExp;
    private String evaluated;
    private int eval;
 
    public ExpSolver(String s)
    {
        list=new ArrayList<String>();
        expression=s;
        trimmedExp=s.trim();
        for (int x=0; x<trimmedExp.length(); x++)
        {
            list.add(""+trimmedExp.charAt(x));
        }
    }
 
    public void setExpression(String s)
    {
        expression=s;
        trimmedExp=s.trim();
        list.clear();
        for (int x=0; x<trimmedExp.length(); x++)
        {
            list.add(""+trimmedExp.charAt(x));
        }        
    }
 
    public void solveExpression()
    {
        eval=0;
        for (int x=0; x<list.size(); x++)
        {
            if (list.get(x).equals("*")||list.get(x).equals("/"))
            {
                if (list.get(x).equals("*"))
                {
                    list.set(x-1, String.valueOf(Integer.parseInt(list.get(x-1))*Integer.parseInt(list.get(x+1))));
                    list.remove(x+1);
                    list.remove(x);
 
                }
 
                else if(list.get(x).equals("/"))
                {
                    list.set(x-1, String.valueOf(Integer.parseInt(list.get(x-1))/Integer.parseInt(list.get(x+1))));
                    list.remove(x+1);
                    list.remove(x);
 
                }
            }
 
        }
 
        for (int x=0; x<list.size(); x++)
        {
            if (list.get(x).equals("-"))
            {
                list.set(x-1, String.valueOf(Integer.parseInt(list.get(x-1))-Integer.parseInt(list.get(x+1))));
                list.remove(x);
                list.remove(x+1);
            }
 
            else if (list.get(x).equals("+"))
            {
                list.remove(x);
            }
        }
        for (int x=0; x<list.size(); x++)
        {
            if (list.get(x).equals(" "))
            {
                list.remove(x);
            }
 
            list.set(x, list.get(x).trim());
        }
 
        for (int x=0; x<list.size(); x++)
        {
            eval+=Integer.parseInt(list.get(x));            
        }
 
        evaluated=String.valueOf(eval);
 
 
    }
 
    public String toString( )
    {
        return evaluated;
    }
}
 
public class Lab04b
{
    public static void main( String args[] )
    {
        ExpSolver test = new ExpSolver("3 + 5");
        test.solveExpression();
        out.println(test.toString());
 
        test.setExpression("3 * 5");
        test.solveExpression();
        out.println(test);
 
        test.setExpression("3 - 5");
        test.solveExpression();
        out.println(test);
 
        test.setExpression("3 / 5");
        test.solveExpression();
     out.println(test);
 
     test.setExpression("5 * 5 + 2 / 2 - 8 + 5 * 5 - 2");
        test.solveExpression();
        out.println(test);
    }
}
 
 

You don't have to import classes in the java.lang package.
The numberFormat exception occurs when you try to convert a string to an Integer (in this case) where the string does not represent a number. You should debug your program with println statements to verify that you are accessing the correct indices if the list because you are currently trying to convert a symbol like +, or / to an int.

[dmjpro]

yes he is right ...
perhaps ur code is trying to parseInt a string which has a character like arithmatic operator....

[rengaraj]

At one point of your program's execution, Integer.parseInt() method gets an argument that is not a valid integer. That's why NumberFormatException is thrown.

Run the program and observe the stack trace for looking into it. You may find out the example for which the program is crashing by running the program for each individual example. Then simulate the code for that example with paper and pencil. I hope you will be able to come up with the mistake you have done.

There are pretty good algorithms for solving arithmetic expressions. You may use one if you find your algorithm incorrect.