Introduction

Believe it or not, performance should not be the first thing on your mind when designing and writing programs. If you prematurely optimize your programs or designs, they will tend to be more complex and error-prone, harder to understand, and more difficult to maintain. Concentrate first on getting a given program to work and adding in the needed features before shifting your focus to how fast it will execute. Otherwise, you can prematurely alter your program by changing the algorithm, adding code to cache results or using different data structures. Another reason not to start optimizing early is that you simply will not know what parts of your program take the most time. Chances are, you'll have to focus on performance at some point because your program is too slow, but that should come later.

If you discover that the application you've developed is slow, the first thing to ask yourself is: Does it really matter? It does if endless tweaking causes your program to ship too late to be useful or if it does not arrive at all. But often, poor performance is more of a nuisance than a disaster. To settle this, you have to time your program using realistic input data, and you have to keep in mind that next year's computers will be twice as fast. If you put your efforts into performance instead of adding needed features and weeding out bugs, you may end up with a fast but useless program.

When you are...