tailieunhanh - Programming Java 2 Micro Edition on Symbian OS A developer’s guide to MIDP 2.0 phần 9

Lớp Xem trong mô hình MV sẽ được quen thuộc với các lập trình viên máy tính để bàn Java GUI (ngay cả khi họ không nhận ra nó), như UI ứng dụng điển hình sử dụng của nó. Ví dụ, các lớp giao diện người dùng hiển thị dưới đây bản chất là một lớp Xem trong mô hình MV | 3 72 WRITING OPTIMIZED CODE Optimizing the LifeEngine Class LifeEngine contains the algorithm that creates the new generation from the old generation. Rather than go through the code line by line it is probably less painful to give a description. The initial implementation used two GenerationMaps one to hold the new generation thisGeneration and one to hold the old generation lastGeneration . looking at the Game of Life rules we have to examine each live cell if it has two or three neighbors it lives so we create a new cell in thisGeneration at the old cell location we also have to examine empty cells that have three neighbors. The way the program does this is to examine every cell adjacent to every live cell if it is empty and has three live neighbors we create a new cell in thisGeneration at the empty location having calculated and displayed the new generation the new generation becomes the old generation and the new generation map is cleared run loops once per generation it goes through all the cells in lastGeneration and calls createNewCell to check whether the cell should live or die and to check if the eight neighboring cells should live or die this translates to a lot of calls to isAlive One significant optimization was applied. testedCells is a GenerationMap used to hold the tested cells. So whenever a cell is checked whether it is empty or not a cell with the same position is created in testedCells. So before testing if a cell should live or die cre-ateNewCell first checks in testedCells to see if it has already been tested if so it does not test it again. This optimization improved the speed of LifeTime by over 30 57s down to 34s . However the extra memory required is significant if there are 200 live cells in a generation there will be some 800 tested cells. At 23 bytes per cell that is about 18 KB. Tools for Optimization a Diversion Taking a guess and test approach to improving performance or reducing memory requirements can work but is .