Creating a prefix notation expression
<p>I'm trying to change an expression to prefix notation. I was able to figure out postfix notation and I was wondering if it was possible to utilize the basic template of my postfix class when creating my prefix class. I'm wanting to take an expression like... 
(6 * ( 24 + 81)) and have an output of: * 6 + 24 81. Is this possible without keeping track of levels?...meaning do I need a tracking variable when my loop enters a parentheses part of the expression? I'm just having a hard time picturing how the structure works. </p>

<p>Here is my postfix code:</p>

<pre><code>    static Stack operatorStack = new Stack();
String ConvertToPostfix(String exp) {
    exp = "("+exp+")";
    int i;
    char token;
    String output = "";

    for (i = 0; i &lt; exp.length(); i++) {
        token = exp.charAt(i);
        if (Character.isLetterOrDigit(token) == true)
            output += token;
        else if (token == '(')
            operatorStack.push(token);
        else if (token == ')') {
            char topChar;
            while ((topChar = peekAtTop()) != '(') {
                output += topChar;
                popAtTop();
            }

        operatorStack.pop();
        } 
        else {
            while (priority(token) &lt;= priority(peekAtTop())) {
                output += peekAtTop();
                popAtTop();
            }
            operatorStack.push(token);
        }
}
    return output;

}
</code></pre>
