Below Example compares the speed of String and StringBuilder Concat Operation
public class PerformanceDemo { public static void main(String[] args) { long now = System.currentTimeMillis(); slow(); System.out.println("slow elapsed " + (System.currentTimeMillis() - now) + " ms"); now = System.currentTimeMillis(); fast(); System.out.println("fast elapsed " + (System.currentTimeMillis() - now) + " ms"); } private static void fast() { StringBuilder s = new StringBuilder(); for (int i = 0; i < 100000; i++) s.append("*"); } private static void slow() { String s = ""; for (int i = 0; i < 100000; i++) s += "*"; } }