Andy Li's Blog

When writing BrainFlash, I was thinking if the string concatenations for program output will slow down the whole interpreter. That is because I was once hit that a year ago when dealing with XML.

I asked for better handling methods over StackOverflow. It is interesting that some of the answers shown that using “+=” is already the fastest. But I still want to know more about that, so I wrote my own simple testing program, which is below:

ActionScript version

Methods used are:

1. str += concateString;
2. str = str.concat(concateString);
3. array.push(concateString); … str = array.join(“”);
4. vector.push(concateString); … str = vector.join(“”);
5. byteArray.writeUTFBytes(concateString); … str = byteArray.readUTFBytes(byteArray.length);
6. byteArray.writeMultiByte(concateString,”us-ascii”); … str = byteArray.readMultiByte(str.length,”us-ascii”);

The result shows that fastest method is using “+=”, but using Array/Vector is still very close to it. Using ByteArray is slow and with ASCII instead of UTF-8 is even slower…

And all the methods are performed reasonably fast, what is slow is when showing the resulting string on TextArea… It takes a few seconds! But when it is drawn, run it again and it will become normal speed, maybe there is some caching?

JavaScript version

I coded a JavaScript port too. See it here.

Methods used are:

1. str += concateString;
2. str = str.concat(concateString);
3. array.push(concateString); … str = array.join(“”);

Interesting enough, the result is very similar to AS3. It is the opposite of what we believe using the Array trick will let it performs faster. “+=” is the fastest in most cases, if not, that’s not much difference.

I’ve only tested in IE8(Win), Firefox 3 (Win/Mac), Safari 4 (Win/Mac), Chrome 3 (Win). The really really really interesting part is in Chrome 3, using the concat method of String is x7000 SLOWER than the other two!! What are your results?