Palindromes?

[llowe29]

My problem is that tthe commented out replace all methods cause errors.

/**
 * Write a description of class RecursivePalindrome here.
 * 
 * @author (Landon L) 
 * @version (12/7/13)
 */
public class RecursivePalindrome
{
    /**
     * Constructor for objects of class RecursivePalindrome
     */
    public RecursivePalindrome()
    {
    }
    public boolean isPalindrome(String word)
    {
        word = isPalindromeHelper(word);
        int a = word.length();
        if(a == 0 || a == 1)
            return true;
        if(word.charAt(0)== word.charAt(a-1))
           return isPalindrome(word.substring(1, a - 1));
        else
        return false;
    }
    public String isPalindromeHelper(String word)
    {
        word = word.toLowerCase();
        word = word.replaceAll(",","");
        word = word.replaceAll(".","");
        word = word.replaceAll("!","");
        word = word.replaceAll(" ","");
        word = word.replaceAll("\"\"","");
        word = word.replaceAll("'","");
        word = word.replaceAll(",","");
        //word = word.replaceAll("?","");
        //word.replaceAll("(","");
        //word.replaceAll(")","");
        return word;  
    }
}

import java.util.*;
public class RecursivePalindromeTester
{
    public static void main(String[] args)
    {
      RecursivePalindrome recP = new RecursivePalindrome();
      Scanner in = new Scanner(System.in);
      System.out.println("Type in word or phrase?(\"q\" to quit)");
      String word = in.next();
      if(word.charAt(0)!='q')
      {
        if(recP.isPalindrome(word))
           System.out.println("This is a palindrome.");
        else
           System.out.println("This isn't a palindrome.");
      }
      else
      {
      System.out.println("Thanks. Come again, later!");   
      System.exit(0);
      }
    }
}

[andbin]

        //word = word.replaceAll("?","");
        //word.replaceAll("(","");
        //word.replaceAll(")","");

replaceAll works with a regular expression and in regexs '?', '(' and ')' are special characters with a specific meaning.

It seems you are not interested in regexs, so use replace(CharSequence target, CharSequence replacement) (Java 5+) instead of replaceAll(). Don't misunderstand the name, replace replaces all occurrences. Simply it doesn't use the concept of regexs.

But if you want to use regexs, you could also create a specific regex to match any of those single chars and replace them with empty string.

Ah, and this:
word = word.replaceAll(".","");

doesn't do what you want. It is correct but '.' in regex means "any character".

[llowe29]

so example of implementation

[andbin]

so example of implementation

Sorry if I repeat myself, but it seems you don't have even basic knowledges on regexs, so my suggestion is to use replace instead of replaceAll.

[llowe29]

thankks ill test it

--- Update ---

it works with word.replace("String", "With Str") no matter how many occurrences but I dont understand how(I mean I dont think it should work

[andbin]

However, if you are curious and want to see a single regex to match all those chars, it's this:

String s = "A,B.C!D E\"F'G?H(I)J";
String s2 = s.replaceAll("[,.! \"'?()]", "");
 
System.out.println(s);
System.out.println(s2);

The regex [ ] is a "character class" and matches any of the characters contained. So [abc] matches 'a' OR 'b' OR 'c'. The good thing of character classes is that many of special characters lose their specific meaning. So outside [ ] the '.' means "any character" while [.] means "the point".

[llowe29]

oh i see my teacehr never mentioned regex but showed us a way to remove all vowels. I didnt realize it worked for everything and could be changed.
this is what I learned string.replaceAll("[aeiou]", "");