java regexp for nested parenthesis

Question

Consider the following java String:

String input = \"a, b, (c, d), e, f, (g, (h, i))\";

Can you help me to find a java regexp to obtain its 6 p

Answer 1

Don't try to use regex for this kind of task since regex in Java doesn't support recursion. Simplest solution would be writing your own parser which would count balance of ( and ) (lets call it parenthesis nesting level) and will split only on , if nesting level would be 0.

Simple code for this task (which will also solve this problem in one iteration) could look like

public static List<String> splitOnNotNestedCommas(String data){
    List<String> resultList = new ArrayList();

    StringBuilder sb = new StringBuilder();
    int nestingLvl = 0;
    for (char ch : data.toCharArray()){
        if (ch == '(') nestingLvl++;
        if (ch == ')') nestingLvl--;
        if (ch == ',' & nestingLvl==0){
            resultList.add(sb.toString().trim());
            sb.delete(0, sb.length());
        }else{
            sb.append(ch);
        }
    }
    if (sb.length()>0)
        resultList.add(sb.toString().trim());

    return resultList;
}

Usage:

for (String s : splitOnNotNestedCommas("a, b, (c, d), e, f, (g, (h, i))")){
    System.out.println(s);
}

Output:

a
b
(c, d)
e
f
(g, (h, i))