这段代码那里出现空指针。请教高手。

cenkongded 2008-07-26 11:21:35

java.lang.NullPointerException

这段代码那里出现空指针。

void introduce(int x)
{
String fn;
fn="/";
fn=fn+Integer.toString(x);
fn=fn+".txt";

InputStream in = getClass().getResourceAsStream(fn);

ByteArrayOutputStream s;
s = new ByteArrayOutputStream(); //产生内存数组输出字节流对象变量S
try{
int ch=0;
ch=in.read(); //由输入流对象变量in的read方法以字节为单位来读取文件的内容，读取到文件尾时的值为-1。
while ( ch!= -1 ) {
//如果未读到文件尾把读取的内容写入S变量中，并读取下一字节内容
s.write( ch );
ch=in.read();
}
in.close(); //关闭输入流对象。
} catch (IOException ioe){
System.out.println(ioe.toString());
}
sr = s.toString(); //将S变量转为字符串
try{
s.close(); //关闭输出流对象
} catch (IOException ioe){
System.out.println(ioe.toString());
}

// phone =new TextField(menu.getTitle(), Sr,4000,0);

// ui_form.append(phone);
myCanvas.setTitle("三国演义");
myCanvas.addCommand(quit);
myCanvas.addCommand(back);
myCanvas.setCommandListener(this);
display.setCurrent(myCanvas);

}

...全文

115 10 打赏收藏转发到动态举报

写回复

用AI写文章

10 条回复

切换为时间正序

请发表友善的回复…

发表回复

xian_hf 2008-07-27

打赏
举报

Canvas myCanvas 没有实例化
在需要用myCanvas.setXXX()之前 new Canvas（）；

都市巴巴 2008-07-26

打赏
举报

my001.introduce(+150)

那么你就在这个introduce方法里面打断点一步一步跟踪吧

cenkongded 2008-07-26

打赏
举报

全部代码。

import java.io.*;
import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;
public class my001 extends MIDlet implements CommandListener
{
private Display display;
private Canvas myCanvas;
Command quit;
Command enter;
Command back;
List menu;

// TextField phone;

String sr;

public my001()
{

display = Display.getDisplay(this);
quit = new Command("退出",Command.EXIT, 3);
enter = new Command("进入", Command.SCREEN, 3);
back=new Command("返回",Command.BACK,3);

}
public void startApp()
{
menu = new List("三国演义", 3);
menu.append("第一章", null);
menu.append("第二章", null);
menu.append("第三章", null);
menu.append("第四章", null);
menu.append("第五章", null);
menu.append("第六章", null);
menu.append("第七章", null);
menu.append("第八章", null);
menu.addCommand(enter);
menu.addCommand(quit);
menu.setCommandListener(this);
display.setCurrent(menu);
}

void introduce(int x)
{
String fn;
fn="/";
fn=fn+Integer.toString(x);
fn=fn+".txt";

InputStream in = getClass().getResourceAsStream(fn);

ByteArrayOutputStream s;
s = new ByteArrayOutputStream(); //产生内存数组输出字节流对象变量S
try{
int ch=0;
ch=in.read(); //由输入流对象变量in的read方法以字节为单位来读取文件的内容，读取到文件尾时的值为-1。
while ( ch!= -1 ) {
//如果未读到文件尾把读取的内容写入S变量中，并读取下一字节内容
s.write( ch );
ch=in.read();
}
in.close(); //关闭输入流对象。
} catch (IOException ioe){
System.out.println(ioe.toString());
}
sr = s.toString(); //将S变量转为字符串
try{
s.close(); //关闭输出流对象
} catch (IOException ioe){
System.out.println(ioe.toString());
}

// phone =new TextField(menu.getTitle(), Sr,4000,0);

// ui_form.append(phone);
myCanvas.setTitle("三国演义");
myCanvas.addCommand(quit);
myCanvas.addCommand(back);
myCanvas.setCommandListener(this);
display.setCurrent(myCanvas);

}

public void setMyCanvas(Canvas myCanvas) {
this.myCanvas = myCanvas;
}
public Canvas getMyCanvas() {
return myCanvas;
}

public void pauseApp()
{

}
public void destroyApp(boolean flag)
{
notifyDestroyed();
}
public void commandAction(Command command, Displayable displayable)
{
if(command == quit)
{

destroyApp(true);

}

else
if(command == enter)
{
List list = (List)display.getCurrent();

// switch(list.getSelectedIndex())
//{
int flag=list.getSelectedIndex();
flag=flag+1;
// case 0: // '\001'
introduce(flag);
// break;
//case 1: // '\001'
// destroyApp(true);
// break;

}
else
if(command==back)
{
display.setCurrent(menu);
}
}

public abstract class myCanvas extends Canvas{
public myCanvas (){

}
public void showNotify(){}
public void hideNotify(){}

public void paint(Graphics g){
g.setColor(128,128,128);
g.fillRect(0,0,getWidth(),getHeight());
g.setColor(120,18,210);
g.setFont(Font.getFont(Font.FACE_PROPORTIONAL,Font.STYLE_BOLD,Font.SIZE_LARGE));
g.drawString(sr, 0,0,Graphics.TOP|Graphics.LEFT);

}

}

}

cenkongded 2008-07-26

打赏
举报

java.lang.NullPointerException
at my001.introduce(+150)
at my001.commandAction(+50)
at javax.microedition.lcdui.Display$DisplayAccessor.commandAction(+282)
at javax.microedition.lcdui.Display$DisplayManagerImpl.commandAction(+10)
at com.sun.midp.lcdui.DefaultEventHandler.commandEvent(+68)
at com.sun.midp.lcdui.AutomatedEventHandler.commandEvent(+47)
at com.sun.midp.lcdui.DefaultEventHandler$QueuedEventHandler.handleVmEvent(+186)
at com.sun.midp.lcdui.DefaultEventHandler$QueuedEventHandler.run(+57)

debug不响应命令按钮。