如何使用J2ME中的线程

如何使用J2ME中的线程

林刚 { lirincy@163.com} 引用需要注明作者，出处

线程在J2ME开发中是不可或缺的一部分，J2ME继承了J2SE中关于java.lang中的Runnable接口，以及Thread类。但是，由于J2ME应用的特殊性，J2ME
程序中去除了部分API，没有线程组的概念，也没有daemon线程。
今天，我们从一个例子出发，来学习J2ME当中的线程的概念。我们选取的例子是俄罗斯方块。首先，有一些要注意的事项：
1.注意一点，要注意在J2me中不要使用浮点数，这样可以通过编译，但是不能通过预验证。因为一般手持设备都无法负担浮点运算的高负荷。
2.在J2ME程序当中，绝大多数的空间为图片所占有，我们可以看到，今天我们的例子没有任何图片，仅仅5k，如果是开发产品，不可避免的要使用图片，
但是尽量使用压缩率高的png图片，而且不要太过复杂，因为复杂的图片会使得图片变得很大。
3.在程序中尽量使用常量特别是位置信息,这样当作修改的时候只要改一个量就可以了,而且当移植到其他平台的时候也会减少很多工作量.还有就是颜色
信息等.不用每次记忆,重新构造,因为J2me中的颜色和j2se的不太一样.没有常量定义.
4.游戏产品经常需要保护版权,而当今的很多反编译工具可以轻而易举地把jar文件的内容反编译过来,因此可以对程序进行模糊化处理,使得无法反编译
或者反编译后无法理解.可以右键点击项目,在属性中选择Build|Obfuscating,选择模糊化级别.
5.讲解中我们都使用NetBeans作为开发平台，有关安装事宜请访问www.netbeans.org.



好，我们开始吧。
A. 首先，建立一个新的移动应用程序项目，取名Tetris, 不要自动创建Hello程序，选取MIDP1.0和CLDC1.0.
B. 新建一个包，方法是右键点击项目，选取New|Java Package,取名Tetris.
C. 新建一个Midlet，同上，选取New|Java Midlet, 取名TetrisMidlet.
D. 我们需要一个能够显示游戏的Canvas, 因此新建一个Class名叫TetrisCanvas, 在TetrisMidlet.java中将TetrisCanvas作为当前可以显示的元素:
现在的TetrisMidlet.java如下:
package Tetris;

import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

/**
*
* @author lin
* @version
*/
public class TetrisMidlet extends MIDlet {
public void startApp() {
Display display = Display.getDisplay( this );
// TetrisCanvas extends Canvas which extends Displayable so it can
// be displayed directly
display.setCurrent( new TetrisCanvas());
}

public void pauseApp() {
}

public void destroyApp(boolean unconditional) {
}
}

由于TetrisCanvas继承了Canvas,所以可以被TetrisMidlet所显示.
E. 这里，我们需要将TetrisCanvas继承Canvas，并且实现Canvas的接口函数paint(),我们现在有了一个TetrisCanvas的框架了。
package Tetris;

import javax.microedition.lcdui.*;
public class TetrisCanvas extends Canvas {
/** Creates a new instance of TetrisCanvas */
public TetrisCanvas() {

}

protected void paint(Graphics g){

}
}

下面我们需要使得TetrisCanvas具有Thread的特性，这里有两种方法，一种是让TetrisCanvas继承Thread类，然后生成它的实例，但是由于它已经
继承了Canvas类，而Java中不允许多重继承，因此，我们在编程当中通常采取第二种做法，也就是让它实现Runnable接口，在成员中声明一个Thread
成员，实例生成指向自己，然后实现run方法。

也就是这样：
public class TetrisCanvas extends Canvas implements Runnable {
private Thread Blocker = null;
...
public TetrisCanvas(){
Blocker = new Thread(this);
Blocker.start();
}

...
public void run(){
while (Blocker != null) {

}

}
...

}
F. 程序逻辑：下面给出程序清单。程序中我们使用一个数组来存储方块的信息,一共有十九种,还有一个数组来存储当前的画面方格的内容.在程序中
有一个paint方法来实现重画,注意绘制的先后次序,当程序规模变得很大的时候,重画的效率就非常重要,需要进行优化.我们在程序中使用了背景,
在没有背景的情况下,程序仅5k,采用背景后,程序47k,可见对图片的优化至关重要.

/*
* TetrisCanvas.java
*
* Created on 2005年7月13日, 上午11:31
*
* To change this template, choose Tools | Options and locate the template under
* the Source Creation and Management node. Right-click the template and choose
* Open. You can then make changes to the template in the Source Editor.
*/

package Tetris;

import java.util.*;
import java.lang.Math;
import javax.microedition.lcdui.*;

/**
*
* @author lin
*/
public class TetrisCanvas extends Canvas implements Runnable{
private Thread Blocker = null;
private Random generator;
private int FutureBlockType, BlockType,LastType,LastX,LastY,BlockX,BlockY ;
private int BlockLines,BlockScore;
private int BlockSpeed,CurSpeed;

private static final int COLOR_GRAY = 0x00eeeeee;
private static final int COLOR_RED = 0x00ff0000;
private static final int COLOR_BLACK = 0x00000000;
private static final int COLOR_WHITE = 0x00ffffff;
private static final int COLOR_BLUE = 0x000000ff;
private static final int COLOR_LIGHT_BLUE= 0x0089a5d1;
private static final int COLOR_DARK_GRAY = 0x00808080;
private static final int COLOR_BACKGROUND= COLOR_LIGHT_BLUE;

private static final int BLOCK_SIZE = 7;
private static final int CANVAS_SIZE_WIDTH = 12;
private static final int CANVAS_SIZE_HEIGHT = 22;
private static final int CANVAS_OFFSET_X = 5;
private static final int CANVAS_OFFSET_Y = 7;

/**
* The paint status.
*/
boolean ISCLEAR = false;
boolean ISDOWN = false;
boolean ISDEL = false;

/**
* the block information matrix.
*/
int BlockInfo[][]={{1,0,1,1,1,2,1,3,0xff0000,2},
{0,1,1,1,2,1,3,1,0xff0000,4},
{0,0,0,1,1,1,1,2,0x0000ff,2},
{0,1,1,0,1,1,2,0,0x0000ff,3},
{0,1,0,2,1,0,1,1,0x00ff00,2},
{0,0,1,0,1,1,2,1,0x00ff00,3},
{0,0,0,1,1,0,1,1,0xffff00,2},
{0,1,1,0,1,1,1,2,0x00ffff,2},
{0,1,1,0,1,1,2,1,0x00ffff,3},
{1,0,1,1,1,2,2,1,0x00ffff,3},
{0,1,1,1,1,2,2,1,0x00ffff,3},
{0,1,0,2,1,1,2,1,0xff00ff,3},
{0,0,1,0,1,1,1,2,0xff00ff,3},
{0,1,1,1,2,0,2,1,0xff00ff,3},
{1,0,1,1,1,2,2,2,0xff00ff,3},
{0,0,0,1,1,1,2,1,0xffffff,3},
{1,0,1,1,1,2,2,0,0xffffff,3},
{0,1,1,1,2,1,2,2,0xffffff,3},
{0,2,1,0,1,1,1,2,0xffffff,3},
};
// Gridmatrix 中只存储颜色信息
int Gridmatrix[][]=new int[CANVAS_SIZE_HEIGHT][CANVAS_SIZE_WIDTH];

/**
* Initialize the applet. Resize and load images.
*/
public void init() {
BlockType=Math.abs(generator.nextInt()%19);
FutureBlockType=Math.abs(generator.nextInt()%19);
LastType=BlockType;

BlockLines=0;
BlockScore=0;
BlockSpeed=1;
CurSpeed=BlockSpeed;
BlockX=4; LastX=BlockX;
BlockY=0; LastY=BlockY;

//初始化Gridmatrix矩阵，内容为带边框的主绘图区。
for(int i=0;i<CANVAS_SIZE_HEIGHT;i++)
for(int j=0;j<CANVAS_SIZE_WIDTH;j++)
Gridmatrix[i][j]=0;
for(int i=0;i<CANVAS_SIZE_WIDTH;i++)
Gridmatrix[CANVAS_SIZE_HEIGHT-1][i]=COLOR_DARK_GRAY;
for(int i=0;i<CANVAS_SIZE_HEIGHT;i++) {
Gridmatrix[i][0]=COLOR_DARK_GRAY;
Gridmatrix[i][11]=COLOR_DARK_GRAY;
}
}

/** Creates a new instance of TetrisCanvas */
public TetrisCanvas() {
generator = new Random( System.currentTimeMillis() );
init();
Blocker = new Thread(this);
Blocker.start();
}

private void draw3DBlock(Graphics g, int c, int x, int y, int width, int height){
int color = g.getColor();
g.setColor( COLOR_WHITE );
g.drawRect( x, y, width, height );
g.setColor(c);
g.fillRect( x + 1, y + 1, width-2, height-2 );
g.setColor( COLOR_BLACK );
g.drawLine( x + width-1, y, x + width-1, y + height-1 );
g.drawLine( x, y + height-1, x + width-1, y + height-1 );
g.setColor(color);
}

public static boolean drawText(Graphics g, String str, int x, int y, int anchor, int color, int size) {
Font f_old,f_new;
int c_old;
try {
f_old = g.getFont();
f_new = Font.getFont(Font.FACE_SYSTEM,Font.STYLE_BOLD,size);
g.setFont(f_new);
c_old = g.getColor();
g.setColor(color);

g.drawString(str, x, y, anchor );

g.setColor(c_old);
g.setFont(f_old);

return true;
}catch (Exception ex) {
return false;
}
}

protected void paint(Graphics g){
//画背景
try{
Image image_Splash = Image.createImage("/back.png");
g.drawImage(image_Splash, 0, 0,Graphics.TOP | Graphics.LEFT);
}
catch(Exception ex) {
}

//画下一个要出现的方块
drawText(g, "下一个", 91, 5, Graphics.TOP| Graphics.LEFT, COLOR_BLUE, Font.SIZE_SMALL);
g.setColor(COLOR_GRAY);
g.drawRoundRect(91, 18, 26, 30, 2, 2);
g.setColor(COLOR_DARK_GRAY);
g.fillRoundRect(92, 19, 24, 28, 2, 2);
for(int i=0;i<=3;i++)
draw3DBlock(g, BlockInfo[FutureBlockType][8],
93+BlockInfo[FutureBlockType][i*2+1]*BLOCK_SIZE,
20+BlockInfo[FutureBlockType][i*2]*BLOCK_SIZE,
BLOCK_SIZE,BLOCK_SIZE);

drawText(g, "速度:"+String.valueOf(CurSpeed), 91, 60, Graphics.TOP| Graphics.LEFT, COLOR_BLUE, Font.SIZE_SMALL);
drawText(g, "行数:"+String.valueOf(BlockLines), 91, 75, Graphics.TOP| Graphics.LEFT, COLOR_BLUE, Font.SIZE_SMALL);
drawText(g, "成绩:", 91, 90, Graphics.TOP| Graphics.LEFT, COLOR_BLUE, Font.SIZE_SMALL);
g.setColor(COLOR_GRAY);
g.drawRoundRect(91, 105, 26, 20, 2, 2);
g.setColor(COLOR_DARK_GRAY);
g.fillRoundRect(92, 106, 24, 18, 2, 2);
drawText(g, String.valueOf(BlockScore), 93, 107, Graphics.TOP| Graphics.LEFT, COLOR_WHITE, Font.SIZE_MEDIUM);

//画当前战况
for(int i=0;i<CANVAS_SIZE_HEIGHT-1;i++)
for(int j=1;j<CANVAS_SIZE_WIDTH-1;j++)
if (Gridmatrix[i][j]!=0)
draw3DBlock(g,Gridmatrix[i][j],CANVAS_OFFSET_X+j*BLOCK_SIZE,
CANVAS_OFFSET_Y+i*BLOCK_SIZE,
BLOCK_SIZE,BLOCK_SIZE);

if (!ISDOWN){
//画上新的方块
LastX=BlockX; LastY=BlockY; LastType=BlockType;
for(int i=0;i<=3;i++)
draw3DBlock(g,BlockInfo[BlockType][8],
CANVAS_OFFSET_X+BlockX*BLOCK_SIZE+BlockInfo[BlockType][i*2+1]*BLOCK_SIZE,
CANVAS_OFFSET_Y+BlockY*BLOCK_SIZE+BlockInfo[BlockType][i*2]*BLOCK_SIZE,
BLOCK_SIZE,BLOCK_SIZE);
}
}

private boolean feasible(){
for(int i=0;i<=3;i++)
if (Gridmatrix[BlockY+BlockInfo[BlockType][i*2]][BlockX+BlockInfo[BlockType][i*2+1]]!=0)
return false;
return true;
}

private void delline(){
for(int i=0;i<=3;i++)
Gridmatrix[BlockY+BlockInfo[BlockType][i*2]][BlockX+BlockInfo[BlockType][i*2+1]]=BlockInfo[BlockType][8];
int temp=4;
boolean CanSkip=false;
int i=CANVAS_SIZE_HEIGHT-2;
while((temp>0)&&(i>=1)){
CanSkip=false;
label1: for(int j=1;j<=CANVAS_SIZE_WIDTH-2;j++){
if (Gridmatrix[i][j]==0) {CanSkip=true; i--; break label1;}
}
if (!CanSkip){
temp--;
for(int k=i;k>=1;k--)
for(int l=1;l<=CANVAS_SIZE_WIDTH-2;l++)
Gridmatrix[k][l]=Gridmatrix[k-1][l];
BlockLines++;
BlockScore+=200;
if((BlockScore%2000)<200) CurSpeed++;
}
}
}

public void run() {
while (Blocker != null) {
if(!ISDOWN){
BlockY++;
if (!feasible()) {
ISDOWN=true; BlockY--; delline();
try {Thread.sleep(400);} catch (InterruptedException e){}
}
else{
repaint();
try {Thread.sleep(950-100*(int)BlockSpeed);} catch (InterruptedException e){}
}
}
else{ BlockScore+=50;
if((BlockScore%2000)<50) CurSpeed++;
ISDOWN=false;
repaint();
BlockSpeed=CurSpeed;
BlockType=FutureBlockType;
FutureBlockType=Math.abs(generator.nextInt()%19);
BlockX=4; LastX=BlockX;
BlockY=0; LastY=BlockY;
if (!feasible()) { init();}
}
}
Blocker = null;
}

protected void keyPressed(int keyCode) {
//处理按下键盘的事件，这是Canvas的实例方法
switch (getGameAction(keyCode)) {//将按键的值转化成方向常量
case Canvas.UP://向上

break;
case Canvas.DOWN://向下
BlockY++;
if (!feasible()) BlockY--;
repaint();
BlockSpeed=9;
//Blocker.run();
break;
case Canvas.LEFT://向左
BlockX--;
if (!feasible()) BlockX++;
break;
case Canvas.RIGHT://向右
BlockX++;
if (!feasible()) BlockX--;
break;
case Canvas.FIRE:
int tempBlockType=BlockType;
if (BlockType==1) BlockType=-1;
else if (BlockType==3) BlockType=1;
else if (BlockType==5) BlockType=3;
else if (BlockType==6) BlockType=5;
else if (BlockType==10) BlockType=6;
else if (BlockType==14) BlockType=10;
else if (BlockType==18) BlockType=14;
BlockType++;
if (!feasible()) BlockType=tempBlockType;
break;
default:
break;
}
repaint(); return;
}
}

参考
J2MEWTK 2.2 documentation.