Java: splitting a comma-separated string but ignoring commas in parentheses

Question

I have a string like this:

one,two,3,(4,five),six,(seven),(8,9,ten),eleven,(twelve,13,14,fifteen)

the above string should split into:

Answer 1

There is a relatively simple, one-line solution to this:

String[] parts = input.split(",(?![^()]*\\))");

Answer 2

Use Regex.

    String s = "one,two,3,(4,five),six,(seven),(8,9,ten),eleven,(twelve,13,14,fifteen)";
    Matcher m = Pattern.compile("[^,()]+|\\([^)]*\\)").matcher(s);
    while (m.find())
        System.out.println(m.group());

Answer 3

The simplest solution to my opinion is to process the input string char-by-char:

public static List<String> split(String input) {
    int nParens = 0;
    int start = 0;
    List<String> result = new ArrayList<>();
    for(int i=0; i<input.length(); i++) {
        switch(input.charAt(i)) {
        case ',':
            if(nParens == 0) {
                result.add(input.substring(start, i));
                start = i+1;
            }
            break;
        case '(':
            nParens++;
            break;
        case ')':
            nParens--;
            if(nParens < 0) 
                throw new IllegalArgumentException("Unbalanced parenthesis at offset #"+i);
            break;
        }
    }
    if(nParens > 0)
        throw new IllegalArgumentException("Missing closing parenthesis");
    result.add(input.substring(start));
    return result;
}

Example:

split("one,two,3,(4,five),six,(seven),(8,9,ten),eleven,(twelve,13,14,fifteen)") ->
[one, two, 3, (4,five), six, (seven), (8,9,ten), eleven, (twelve,13,14,fifteen)]

As a free bonus, this solution also counts nested parentheses if necessary:

split("one,two,3,(4,(five,six),seven),eight") ->
[one, two, 3, (4,(five,six),seven), eight]

Also it checks whether parentheses are balanced (every open parenthesis has the corresponding closing one).

Answer 4

here you go... :)

import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

/**
 *
 * @author S1LENT W@RRIOR
 */
public class Tokenizer {

    public static void main(String... args) {

        List<String> tokens = new ArrayList(); // List to store tokens

        String string = "one,two,3,(4,five),six,(seven),(8,9,ten),eleven,(twelve,13,14,fifteen)"; // input string
        StringTokenizer tokenizer = new StringTokenizer(string, "(),", true); // tokenize your string on the basis of these parentheses 

        while (tokenizer.hasMoreElements()) { // iterate over tokens

            String aToken = (String) tokenizer.nextElement(); // get a token

            if (aToken.equals("(")) { // if token is the begining of a parenthisis
                StringBuilder sb = new StringBuilder(aToken);
                String nextToken = (String) tokenizer.nextElement(); // get next token
                while (!nextToken.equals(")")) { // iterate over next tokens untill you find the ending bracket
                    sb.append(nextToken);
                    nextToken = (String) tokenizer.nextElement();
                }
                sb.append(")");

                tokens.add(sb.toString()); // add to tokens list
            } else if(aToken.equals(",")) { // need this to avoid adding commas
                // do nothing
            } else {
                tokens.add(aToken); // add to tokens list
            }
        }

        for(String aToken: tokens) { // print all tokens
            System.out.println(aToken);
        }
    }
}