1．MIDP中的特定类和接口
1) Javax.microedition.midlet-----是最内层的包，只包含一个MIDlet类,它为MIDP应用提供了基本功能开支
2) javax.microedition.io-----包括HTTPConnection接口，通过这个接口，MIDlet设备可访问Web中的数据
3) javax.microedition.lcdui(Liquid Crystal Display User Interface液晶显示用户界面)-----对GUI组件提供支持，有与java.awt同样的功能，javax.microedition.lcdui包中的类和接口更适用与小屏幕的手持设备.
4) javax.microedition.rms(记录治理系统)-----支持数据库系统的不同类和接口，它们随后存储和检索MIDlet所用的数据
2. 一个实例:
1) 任务陈述-----SaveMyMoney银行的移动应用系统第一个屏幕显示欢迎消息，第二个屏幕上应该显示当前日期，当前时间，总的内存，以及自由内存
2) 实现代码如下:
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
import java.util.*;
public class MB extends MIDlet implements CommandListener
{
Display display;
Form form1;
Form form2;
Ticker ticker1;
static final Command okCommand = new Command("Info",Command.OK,1);
static final Command backCommand = new Command("Back",Command.BACK,0);
static final Command exitCommand = new Command("Exit", Command.STOP, 2);
public MB()
{
}
public void startApp() throws MIDletStateChangeException
{
display = Display.getDisplay(this);
ticker1=new Ticker("Welcome to the World of Mobile Banking!");
form1 = new Form("SaveMyMoney");
form2 = new Form("INFORMATION");
Calendar calendar1 = Calendar.getInstance();
int date=calendar1.get(Calendar.MONTH);
String date1 = Integer.toString (calendar1.get(Calendar.DAY_OF_MONTH)) + "" +
Integer.toString(calendar1.get(Calendar.YEAR));
String time = Integer.toString(calendar1.get(Calendar.HOUR_OF_DAY)) + ":" +
Integer.toString(calendar1.get(Calendar.MINUTE)) + ":" +
Integer.toString(calendar1.get(Calendar.SECOND));
Runtime runMemory = Runtime.getRuntime();
String total_Memory = Long.toString(runMemory.totalMemory());
String free_Memory = Long.toString(runMemory.freeMemory());
String month =" 0";
switch(date)
{
case 0: month="January";break;
case 1: month="February";break;
case 2: month="March";break;
case 3: month="April";break;
case 4: month="May";break;
case 5: month="June";break;
case 6: month="July";break;
case 7: month="August";break;
case 8: month="September";break;
case 9: month="October";break;
case 10: month="November";break;
case 11: month="December";break;
}
StringItem strItem = new StringItem("Welcome toSaveMyMoney Bank!", "");
form1.append(strItem);
form2.append(new StringItem(" ", "DATE: "+ month +",")) ;
form2.append(date1);
form2.append(new StringItem(" ", "TIME:" + time));
form2.append(new StringItem(" ", "Total Memory:" + total_Memory));
form2.append(new StringItem(" ", "Free Memory:" + free_Memory));
form1.addCommand(exitCommand);
form1.addCommand(okCommand);
form1.setCommandListener(this);
form1.setTicker(ticker1);
display.setCurrent(form1);
}
public void pauseApp()
{
}
public void destroyApp(boolean unconditional)
{
notifyDestroyed();
}
public void showForm1()
{
form1.addCommand(exitCommand);
form1.addCommand(okCommand);
form1.setCommandListener(this);
display.setCurrent(form1);
}
public void showForm2()
{
form2.addCommand(exitCommand);
form2.addCommand(backCommand);
form2.setCommandListener(this);
display.setCurrent(form2);
}
public void commandAction(Command c, Displayable d)
{
String label = c.getLabel();
if (label.equals("Exit"))
{
destroyApp(true);
}
else if (label.equals("Back"))
{
// go back to Form1
showForm1();
}
else
{
showForm2();
}
}
}
