## A Practical Guide

Many useful techniques exist for optimizing a Java program. Instead of
focusing on one particular technique, this article considers the
optimization process as a whole. Authors Erwin Vervaet and Maarten De
Cock walk readers through the performance tuning of a puzzle-solving
program, applying an assortment of techniques ranging from simple
technical tips to more advanced algorithm optimizations. The end result
is a spectacular performance increase (more than a *million* fold) between the first working implementation and the fully optimized solution.

Most Java performance-related articles focus on the many techniques that
programmers can employ to speed up their programs. At one end of the
spectrum you can find descriptions of relatively simple programming
idioms, like the use of the `StringBuffer`

class. At the other end you find discussions of more advanced
techniques, like the use of object caches. Instead of adding to this
list of techniques, we'll present a practical example that combines
them to speed up a puzzle-solving program.

The program we will develop and optimize calculates all possible solutions for the Meteor puzzle, a brain teaser consisting of 10 puzzle pieces, each a different color made up of five hexagons (six-sided polygons with each side of equal length). The puzzle board itself is a rectangular grid of 50 hexagons laid out in a 5-by-10 pattern. You solve the puzzle by covering the entire board using the 10 available pieces. A possible solution to this puzzle is shown in Figure 1.

While the Java program discussed in this article solves the 10-piece Meteor puzzle, the real goal was to solve a much larger 209-piece puzzle called the Eternity puzzle, devised by Christopher Monckton and introduced in Britain in June 1999. At the same time that Eternity was released, Monckton released various smaller puzzles: Meteor, Delta, and Heart. By solving any of these puzzles, a player could send off for one of various hints that showed where on the Eternity grid particular pieces were located in Monckton's solution. A £1 million award (approximately $1.5 million USD) was offered for the first person who solved the Eternity puzzle, which was finally collected by Alex Selby and Oliver Riordan on May 15, 2000. A second solution was later found by Guenter Stertenbrink. Interestingly, neither of these solutions matched the six clues given by Christopher Monckton for his solution, which remains unknown. |

**Figure 1. A solution for the Meteor puzzle**

As simple as finding this solution might seem, it is a non-trivial
problem to implement in a computer program. Writing that program will
be a refreshing change from the contrived examples you can find in many
other Java performance-related articles. It allows us to illustrate a
number of different optimization techniques and the ways of combining
them. However, before we start optimizing, we first need to develop a
working solution.

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