java 代码细节（Substitute Algorithm）

这个观点来自《重构-----改善既有代码的设计》

You want to replace an algorithm with one that is clearer.

02

Replace the body of the method with the new algorithm.

03

String foundPerson(String[] people){
    for (int i = 0; i < people.length; i++) {
        if (people[i].equals ("Don")){
            return "Don";
        }
        if (people[i].equals ("John")){
            return "John";
        }
        if (people[i].equals ("Kent")){
            eturn "Kent";
        }
    }
    return "";
}

04

String foundPerson(String[] people){
    List candidates = Arrays.asList(new String[] {"Don", "John", "Kent"});
    for (int i=0; i<people.length; i++)
        if (candidates.contains(people[i]))
            return people[i];
    return "";
}

Motivation

05

I’ve never tried to skin a cat. I’m told there are several ways to do it. I’m sure some are easier than others. So it is with algorithms. If you find a clearer way to do something, you should replace the complicated way with the clearer way. Refactoring can break down something complex into simpler pieces, but sometimes you just reach the point at which you have to remove the whole algorithm and replace it with something simpler. This occurs as you learn more about the problem and realize that there’s an easier way to do it. It also happens if you start using a library that supplies features that duplicate your code.

06

Sometimes when you want to change the algorithm to do something slightly different, it is easier to subtitute the algorithm first into something easier for the change you need to make.

07

When you have to take this step, make sure you have decomposed the method as much as you can. Substituting a large, complex algorithm is very difficult; only by making it simple you can make the substitution tractable.

Mechanics

08

• Prepare your alternative algorithm. Get it so that it compiles.
• Run the new algorithm against your tests. If the results are the same, you’re finished.
• If the results aren’t the same, use the old algorithm for comparison in testing and debugging.

  Run each test case with old and new algorithms and watch both results. That will help you see which test cases are causing trouble, and how.