unable to correctly validate balanced parenthesis parsing in java method

Question

I have a method that\'s supposed to validate accurate opening and closing parenthesis in a string using java. This method will be used to parse mathematical expressions so it\'s

Answer 1

As far as I can tell, there is no problem with the code (turns out it's a Java 7 specific issue..).

I would like to offer a replacement method though, for educational purposes, that is shorter, and and is tolerant of other characters being present:

public static boolean parChecker(String str) {
    Stack stack = new Stack(str.length());
    for (char c : str.toCharArray())
        switch (c) {
        case '(':
            stack.push(c);
            break;
        case ')':
            if (stack.isEmpty() || stack.pop() != Character.valueOf('('))
                return false;
        }
    return stack.isEmpty();
}

As requested, here's another solution that doesn't use a stack:

public static boolean parChecker(String str) {
    str = str.replaceAll("[^()]", "");
    while (str.contains("()"))
        str = str.replace("()", "");
    return str.isEmpty();
}

And one more for the road: @FredK's algorithm:

public static boolean parChecker(String str) {
    int depth = 0;
    for ( char c : str.toCharArray() )      
        if ( ( depth += c == '(' ? 1 : c == ')' ? -1 : 0 ) < 0 )
            return false;
    return depth == 0;
}

Answer 2

The immediate problem is this

String[] tokens = str.split("");

Gives you first char = "" if you use java 1.7 or less, so you will exit your loop since stack is empty...

Note: this has been changed in java 1.8 split difference between java 1.7 and 1.8

change to:

char[] tokens = str.toCharArray();

I guess however that you need to consider the fact that there can be chars before your first ( and that you may have other chars then ( and )