If you’re building a long String in Java, don’t stick String objects together using ‘+’, for example:
String str = "Hello"; str = str + world; str = str + "!";
It’s really slow when you do it a lot!
What should you do instead?
Use the append(String) method in StringBuffer (Java 1.4.2 on), or StringBuilder (Java 5 on). StringBuilder is slightly faster than StringBuffer, but is not thread safe. Both are much faster than concatenating String objects – by orders of magnitude. For example:
StringBuffer str = new StringBuffer("Hello"); str.append(world); str.append("!");