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Is it better to reuse a StringBuilder in a loop?

Asked 2008-10-28T07:09:37.790
110

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 this:

for (loop condition) {
    StringBuilder sb = new StringBuilder();
    sb.append("some string");
    . . .
    sb.append(anotherString);
    . . .
    passToMethod(sb.toString());
}

Is instantiating StringBuilder at every loop cycle is a good solution? And is calling a delete instead better, like the following?

StringBuilder sb = new StringBuilder();
for (loop condition) {
    sb.delete(0, sb.length);
    sb.append("some string");
    . . .
    sb.append(anotherString);
    . . .
    passToMethod(sb.toString());
}
java performance string stringbuilder
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1 Answer

1

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 );
answered 2013-06-05T13:53:05.123

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