java - Optimize this ArrayList join method

Question

I have written this code to join ArrayList elements: Can it be optimized more? Or is there a better different way doing this?

public static String join(ArrayList list, char delim) {
        StringBuffer buf = new StringBuffer();
        for (int i = 0; i < list.size(); i++) {
            if (i != 0)
                buf.append(delim);
            buf.append((String) list.get(i));
        }
        return buf.toString();
    }

Answer 1

StringBuffer is synchronized for thread safety, use a StringBuilder instead.

Don't call list.size() each iteration of the loop. Either set it as a variable or use an Iterator.

Also note that there are lot of libraries for doing this, chiefly google collections. Try the following:

public String join(List<?> list, char delimiter) {
    StringBuilder result = new StringBuilder();
    for (Iterator<?> i = list.iterator(); i.hasNext();) {
        result.append(i.next());
        if (i.hasNext()) {
            result.append(delimiter);
        }
    }
    return result.toString();
}