java - Why use append() instead of + -

possible duplicate:
why use stringbuffer in java instead of string concatenation operator

what advantage or aim of doing this

int a= 42 stringbuffer sb = new stringbuffer(40);  string s = sb.append("a = ").append(a).append("!").tostring();  system.out.println(sb); 

result > = 42!

instead of

 int a= 42  string s = "a = " + + "!";   system.out.println(sb); 

in scenario, i'm not sure there difference b/c of "+" on 1 line (which believe creates 1 string). in general, though, strings immutable objects , not manipulated rather created , discarded using stringbuffers.

so ultimately, have more efficient code if use stringbuffers (and stringbuilders). if google "string vs. stringbuffer vs. stringbuilder" can find many articles detailing statistics.