Programming Optimizations

A final possible step in the optimization process for our puzzle-solving program is the use of low-level Java code optimization idioms. We're not manipulating any strings in our application, so applying the well-known StringBuffer idiom is useless. We could try to avoid the method call overhead for getters and setters by replacing those getters and setters with direct member access. However, this clearly degrades the quality of our code and tests show that this hardly generates any speedup at all. The same is true for the use of final methods. By declaring our methods as final, we avoid dynamic binding and allow the Java virtual machine to use more efficient static binding. But alas, this does not produce any noticeable speedup. Also, the use of the -O optimization switch of the Java compiler does not produce any real performance increase.

A slight execution speedup can still be obtained by improving the implementation of the prune() method. The code in Listing 7 always makes a call to the recursive getIslandSize() method, even if the board cell is already processed or is not empty. If we proactively do these checks before invoking getIslandSize(), we gain about 10 percent.

As is clear from this discussion, low-level optimizations result in very small performance increases. This, combined with the fact that some of these optimization techniques deteriorate the quality of your code, makes the use of low-level optimizations unappealing.