Use StringBuilder.append instead of += when building up a String.

[kevinsawicki]

This reduces the number of total String objects created and keeps the same contents in a StringBuilder instance instead.

[bwmcadams]

Java's compiler automatically does this optimization for you since either 5 or 6, so not necessary.

[kevinsawicki]

Then why do so many other places in the mongo-java-driver use StringBuilder.append instead of += on String objects? These were the only 3 classes that use +=.

[kevinsawicki]

Try running both of these and see if you get the same amount of time to complete:

public static void main( String[] args ) {
    long start = System.currentTimeMillis();
    String a = "test";
    for ( int i = 0; i < 10000; i++ ) {
        a += Integer.valueOf( i ).toString();
    }
    System.out.println( System.currentTimeMillis() - start );
}

public static void main( String[] args ) {
    long start = System.currentTimeMillis();
    StringBuilder a = new StringBuilder( "test" );
    for ( int i = 0; i < 10000; i++ ) {
        a.append( Integer.valueOf( i ).toString() );
    }
    System.out.println( System.currentTimeMillis() - start );
}

[mebigfatguy]

The java compiler will replace += with StringBuilder, but kevin is right. His code only generates one new StringBuilder(), many append calls, and one toString call. Whereas, the a += ... generates 'n' new StringBuilder() calls, the same number of appends, and 'n' toString calls.

Creates alot of garbage

btw kevin, the toString() call on the Integer is superfluous when calling append.

[bwmcadams]

I stand corrected. Ill reopen this shortly. Thanks for the clarifications as
well.
On Jul 29, 2011 8:33 PM, "mebigfatguy" <
[email protected]>
wrote:

The java compiler will replace += with StringBuilder, but kevin is right.
His code only generates one new StringBuilder(), many append calls, and one
toString call. Whereas, the a += ... generates 'n' new StringBuilder()
calls, the same number of toStrings, and 'n' toString calls.

Creates alot of garbage

Reply to this email directly or view it on GitHub:
#39 (comment)

[kevinsawicki]

btw kevin, the toString() call on the Integer is superfluous when calling append.

Yes, I am aware of that, I was just trying to create a simple but explicit example of appending a String to a String.

Is this pull request going to be reopened?