Is it better to reuse a StringBuilder in a loop?

Question

I\'ve a performance related question regarding use of StringBuilder. In a very long loop I\'m manipulating a StringBuilder and passing it to another method like

Answer 1

The modern JVM is really smart about stuff like this. I would not second guess it and do something hacky that is less maintainable/readable...unless you do proper bench marks with production data that validate a non-trivial performance improvement (and document it ;)

Answer 2

Not significantly faster, but from my tests it shows on average to be a couple millis faster using 1.6.0_45 64 bits: use StringBuilder.setLength(0) instead of StringBuilder.delete():

time = System.currentTimeMillis();
StringBuilder sb2 = new StringBuilder();
for (int i = 0; i < 10000000; i++) {
    sb2.append( "someString" );
    sb2.append( "someString2"+i );
    sb2.append( "someStrin4g"+i );
    sb2.append( "someStr5ing"+i );
    sb2.append( "someSt7ring"+i );
    a = sb2.toString();
    sb2.setLength(0);
}
System.out.println( System.currentTimeMillis()-time );