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Delimeter Check

Posted on 2003-10-24
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Last Modified: 2012-05-04
I need help with this:

Write a class method named 'DelimMatch' and a method main that will test it

The method 'match' will take a String that may contain any number of parentheses, brackets, or braces as a parameter and return true if the parentheses, brackets, or braces are balanced and false if they are not.

It is giving one error and I need help setting it up for braces as well(I have brackets and parentheses already)

import java.io.*;
import java.util.Stack;

public class DelimMatch
{
    public static void main (String [] args) throws java.io.IOException
    {
        System.out.println("Enter expression: ");
      BufferedReader d = new BufferedReader(new InputStreamReader(System.in));
      String line = d.readLine();

        Stack parens = new Stack();
      
        for (int i = 0; i < line.length(); i++)
        {
            if (line.charAt(i) == '(' || line.charAt(i) == '[')
            {
                parens.push(new Character(line.charAt(i)));
            }
            else if (line.charAt(i) == ')' || line.charAt(i) == ']')
            {
            if (parens.empty())
                {
                    System.out.println("Error: unmatched right delimeter at index " + i);
                    return;
            }
            else
                {
                    Character top = (Character)parens.pop();
                    if (!match(top.charValue(), line.CharAt(i)))
                    {
                        System.out.println("Error: mismatched delimeters at index " + i);
                  return;
                    }
            }
            }
      }
      if (!parens.empty())
        {
            System.out.println("Error: unclosed left delimeter");
      }
      else
        {
            System.out.println("Expression is OK");
      }
    }
      
    private static boolean match(char ch1, char ch2)
    {
        return ((ch1 == '(' && ch2 == ')') || (ch1 == '[' && ch2 == ']'));
    }
}


help please

rbg
0
Comment
Question by:rbgerman
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11 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 9617890
What about nesting?
0
 
LVL 5

Expert Comment

by:lwinkenb
ID: 9618298
>>It is giving one error

what is the error?
0
 
LVL 5

Accepted Solution

by:
lwinkenb earned 50 total points
ID: 9618315
hmm.. I copied you code, and changed
if (!match(top.charValue(), line.CharAt(i)))
to
if (!match(top.charValue(), line.charAt(i))) // notice the lower case 'c'

Now it seems to work just fine.  To add braces, just do it the same way you do brackets and parenthesis:
 if (line.charAt(i) == '(' || line.charAt(i) == '[' || line.charAt(i) == '{')

You should be able to get it from there.  If not, post where you are still having trouble.
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LVL 1

Author Comment

by:rbgerman
ID: 9629684
hey thanks...can't believe I missed that.  I stared at it for an our wondering why that charAt was giving me fits (damn case sensitivity).  I will award the points to you..can you help with one thing though.  I have slightly changed the code...but now I would really like a while loop to allow the user to enter as many expressions or Strings as they want.  Could you help me do that please?

Here is the modified code:

import java.util.Stack;
import TerminalIO.KeyboardReader;

public class DelimMatch
{
    public static void main (String [] args)
    {
        KeyboardReader reader = new KeyboardReader();
       
        String line = reader.readLine("Enter expression: ");

        Stack parens = new Stack();
      
        for (int i = 0; i < line.length(); i++)
        {
            if (line.charAt(i) == '(' || line.charAt(i) == '[')
            {
                parens.push(new Character(line.charAt(i)));
            }
            else if (line.charAt(i) == ')' || line.charAt(i) == ']')
            {
            if (parens.empty())
                {
                    System.out.println("Error: unmatched right delimeter at index " + i);
                    return;
            }
            else
                {
                    Character top = (Character)parens.pop();
                    if (!checkDelimeters(top.charValue(), line.charAt(i)))
                    {
                        System.out.println("Error: mismatched delimeters at index " + i);
                  return;
                    }
            }
            }
      }
      if (!parens.empty())
        {
            System.out.println("Error: unclosed left delimeter");
      }
      else
        {
            System.out.println("Expression is OK");
      }
       
    }
      
    private static boolean checkDelimeters(char ch1, char ch2)
    {
        return ((ch1 == '(' && ch2 == ')') || (ch1 == '[' && ch2 == ']'));
    }
}


thanks

rbg
0
 
LVL 5

Expert Comment

by:lwinkenb
ID: 9630588
just place a while loop around the code in the main method:

import java.util.Stack;
import TerminalIO.KeyboardReader;

public class DelimMatch
{
    public static void main (String [] args)
    {
        while(true) {
              KeyboardReader reader = new KeyboardReader();
              
              String line = reader.readLine("Enter expression: ");
      
              Stack parens = new Stack();
          
              for (int i = 0; i < line.length(); i++)
              {
                  if (line.charAt(i) == '(' || line.charAt(i) == '[')
                  {
                      parens.push(new Character(line.charAt(i)));
                  }
                  else if (line.charAt(i) == ')' || line.charAt(i) == ']')
                  {
                            if (parens.empty())
                      {
                          System.out.println("Error: unmatched right delimeter at index " + i);
                          return;
                            }
                            else
                      {
                          Character top = (Character)parens.pop();
                          if (!checkDelimeters(top.charValue(), line.charAt(i)))
                          {
                              System.out.println("Error: mismatched delimeters at index " + i);
                                       return;
                          }
                            }
                  }
                 }
                   if (!parens.empty())
                     {
                         System.out.println("Error: unclosed left delimeter");
                     }
                    else
                    {
                        System.out.println("Expression is OK");
                    }
            }  
    }
     
    private static boolean checkDelimeters(char ch1, char ch2)
    {
        return ((ch1 == '(' && ch2 == ')') || (ch1 == '[' && ch2 == ']'));
    }
}
0
 
LVL 1

Author Comment

by:rbgerman
ID: 9634246
i guess what i am asking is ...
how can i set it up to start out with...

"do you want to enter another expression? (Y or N)"
Y
enter it

answer

"do you want to enter another expression? (Y or N)"
N
exit

please help me out...i am confused a bit

rbg
0
 
LVL 1

Author Comment

by:rbgerman
ID: 9634379
i went ahead and awarded you then points before i forgot....

the while loop does work...but I needed some guidance in making it ask:

"do you want to enter another expression? (Y or N)"

so it will exit

please help me out here

rbg
0
 
LVL 5

Expert Comment

by:lwinkenb
ID: 9635284
change it to this:

boolean loop = true;

while(loop) {
  //The delim code goes here
  System.out.println("do you want to enter another expression? (Y or N)");
  String res = //user input
  if(!res.ignoreCase.equals("y"))
    loop = false;
}
0
 
LVL 1

Author Comment

by:rbgerman
ID: 9637076
thanks man...awesome

i see how that is set up now

rbg
0
 
LVL 1

Author Comment

by:rbgerman
ID: 9637733
it's actually still not looping...

if i type Y or y it still ends???  here is the final code with the loop additions...hope you still want to help

import java.util.Stack;
import TerminalIO.KeyboardReader;

public class DelimeterCheck
{
    public static void main (String [] args)
    {
        boolean loop = true;
       
        while (loop)
        {        
        KeyboardReader reader = new KeyboardReader();      
        String line = reader.readLine("Enter expression: ");
        Stack parens = new Stack();
      
        for (int i = 0; i < line.length(); i++)
        {
            if (line.charAt(i) == '(' || line.charAt(i) == '[' || line.charAt(i) == '{')
            {
                parens.push(new Character(line.charAt(i)));
            }
            else if (line.charAt(i) == ')' || line.charAt(i) == ']' || line.charAt(i) == '}')
            {
            if (parens.empty())
                {
                    System.out.println("Error: unmatched right delimeter at index " + i);
                    return;
            }
            else
                {
                    Character top = (Character)parens.pop();
                    if (!checkDelimeters(top.charValue(), line.charAt(i)))
                    {
                        System.out.println("Error: mismatched delimeters at index " + i);
                  return;
                    }
            }
            }
      }
      if (!parens.empty())
        {
            System.out.println("Error: unclosed left delimeter");
      }
      else
        {
            System.out.println("Expression is OK");
      }          
       
        System.out.println("Do you want to enter another expression? (Y or N)");
        String res = reader.readLine();
        if(!res.equals("y") || !res.equals("Y")) loop = false;        
        }
    }
      
    private static boolean checkDelimeters(char ch1, char ch2)
    {
        return ((ch1 == '(' && ch2 == ')') || (ch1 == '[' && ch2 == ']') || (ch1 == '{' && ch2 == '}'));
    }
}

rbg
0
 
LVL 5

Expert Comment

by:lwinkenb
ID: 9637854
>>if(!res.equals("y") || !res.equals("Y"))
That conditional statement will ALWAYS return true.  It should be:
if(!res.equals("y") && !res.equals("Y"))
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