Palindrome checker

[thirdage]

I want to check if a phrase is a palindrome.
For example (H ell o o l l e h)
I wanna write a method that skip spaces as it reads from left and as it reads from right.

public static boolean PalindromeChecker(String str)
	{
		boolean mismatch = false;
		int len = str.length();
		int i =0;
		int j = len -1;
		while (i<j && !mismatch )
		{
			String lowerCased = str.toLowerCase();
			if (lowerCased.charAt(i)==lowerCased.charAt(j))
			{
				mismatch =false;
			}
			else
			{
				mismatch = true;
			}
			i = i+1;
			j=j-1;

		}
		return mismatch;

	}

My question is where should I enter the statement that would cancel spaces as i go from left and as i go from the right?
and is it an if statement .. or another loop?
Thanks a lot in advance!!

[gcalvin]

Pseudocode:

    int startpos = 0
    while (char at startpos is not a letter)
        increment startpos

    int endpos = mystring.length
    while (char at endpos is not a letter)
        decrement endpos

Consider using a recursive approach. Maybe a boolean isPalindrome(char[] myCharArray, int startpos, int endpos) method.

[JosAH]

You could define two small methods:

int decrement(String, s, int i) { ... }
int increment(String s, int i) { ... }

... that decrement or increment index value i until s[i] isn't a white space character or until i is an out of bounds index; if it is out of bounds the methods return -1 to signal that event. In your loop you increment i and decrement j until one of them is -1 or until i >= j.

kind regards,

Jos

[thirdage]

I didn't learn the recursive approach yet ... for now i must do this in loops and if statements!

[gcalvin]

A few other things... PalindromeChecker is a good name for the class, but a bad name for this method. boolean isPalindrome(String string) would be better. Style is important, and a method name should be a verb and should start with a lower-case letter. Also you're going to confuse yourself with that variable named mismatch. Consider converting your whole string to upper case right at the beginning, and then convert that to a char[]. Then you can do:

    while (endpos > startpos)
        while (char at startpos is not a letter)
            increment startpos
            if (startpos == endpos) return true

        while (char at endpos is not a letter)
            decrement endpos
            if (startpos == endpos) return true

        if (char at startpos doesn't match char at endpos) return false

    if loop completes return true (it means that you've met in the middle)