我有一个程序，目前除了显示时间并允许用户按下一个按钮，该按钮将引导他进入另一个屏幕，我将显示一个对话框以显示成功运行（仅供参考，应用程序的名称是 SuperAlarms，我正在使用 Eclipse 插件）。该程序编译得非常好（尽管有一些错误表明某些变量没有被使用）但是一旦我加载程序我得到一个“java.lang.NullPointerException”。
超级警报.java：
/*
* Description:
* A convenient alarm clock application that will play a song and provide a "pause" button
* to pause the music so it can be continued later
* Author: Dennis Plotnik
* Copyright: Standard Intellectual Property Copyright Laws Apply (2012)
* Version: 1.0
* Methods used:
* - Date
* - Threads
* - Music Streams
* - GUI
*
*/
package com.galaxy.dennis;
import net.rim.device.api.ui.UiApplication;
/**
* This class extends the UiApplication class, providing a
* graphical user interface.
*/
public class SuperAlarms extends UiApplication
{
/**
* Entry point for application
* @param args Command line arguments (not used)
*/
public static void main(String[] args)
{
// Create a new instance of the application and make the currently
// running thread the application's event dispatch thread.
SuperAlarms theApp = new SuperAlarms();
theApp.enterEventDispatcher();
}
/**
* Creates a new SuperAlarms object
*/
public SuperAlarms()
{
// Push a screen onto the UI stack for rendering.
pushScreen(new SuperAlarmsMainScreen());
}
}
SuperAlarmsMainScreen.java：
package com.galaxy.dennis;
import net.rim.device.api.ui.Field;
import net.rim.device.api.ui.FieldChangeListener;
import net.rim.device.api.ui.Font;
import net.rim.device.api.ui.FontFamily;
import net.rim.device.api.ui.Ui;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.component.ButtonField;
import net.rim.device.api.ui.component.Dialog;
import net.rim.device.api.ui.component.LabelField;
import net.rim.device.api.ui.component.SeparatorField;
import net.rim.device.api.ui.container.HorizontalFieldManager;
import net.rim.device.api.ui.container.MainScreen;
/**
* A class extending the MainScreen class, which provides default standard
* behavior for BlackBerry GUI applications.
*/
public final class SuperAlarmsMainScreen extends MainScreen implements FieldChangeListener
{
private TimeUpdater updater;
private HorizontalFieldManager hfm_centerTime;
private Alarm[] alarms;
private ButtonField bf_newAlarm;
private GridOrganizer g;
private FontFamily comicSansMs;
private Font fnt_title;
private Font fnt_main;
//LabelFields
private LabelField lf_curTime;
public SuperAlarmsMainScreen()
{
//FieldManagers
hfm_centerTime = new HorizontalFieldManager(Field.FIELD_HCENTER);
g = new GridOrganizer(0, null);
//Fonts:
try {
comicSansMs = FontFamily.forName("Comic Sans MS");
fnt_title = comicSansMs.getFont(Font.BOLD, 16, Ui.UNITS_pt);
fnt_main = comicSansMs.getFont(Font.PLAIN, 12, Ui.UNITS_pt);
} catch(ClassNotFoundException e) { e.printStackTrace(); }
//Title:
setTitle("SuperAlarms");
//Updater:
for (int i=0;i<5;i++) alarms[i] = new Alarm(null, null, null, null);
updater = new TimeUpdater(alarms);
updater.start();
//Labelfields:
lf_curTime = new LabelField(updater.getTime());
lf_curTime.setFont(fnt_title);
hfm_centerTime.add(lf_curTime);
add(hfm_centerTime);
add(new SeparatorField());
//Bottom
bf_newAlarm = new ButtonField("Create New Alarm", ButtonField.CONSUME_CLICK);
bf_newAlarm.setChangeListener(this);
}
public void fieldChanged(Field field, int context) {
if (field == bf_newAlarm) {
UiApplication.getUiApplication().pushScreen(new NewAlarmScreen());
}
}
}
NewAlarmScreen.java：
package com.galaxy.dennis;
import net.rim.device.api.ui.component.Dialog;
import net.rim.device.api.ui.container.MainScreen;
public class NewAlarmScreen extends MainScreen {
public NewAlarmScreen() {
Dialog.alert("You clicked that button!");
}
}
GridOrganizer.java：
package com.galaxy.dennis;
import net.rim.device.api.ui.Field;
import net.rim.device.api.ui.component.SeparatorField;
import net.rim.device.api.ui.container.HorizontalFieldManager;
import net.rim.device.api.ui.container.MainScreen;
import net.rim.device.api.ui.container.VerticalFieldManager;
public class GridOrganizer {
private HorizontalFieldManager[] hfm;
private VerticalFieldManager[] vfm;
private int row;
private MainScreen screen;
public GridOrganizer(int row, MainScreen mainscreen) {
this.row = row;
this.screen = mainscreen;
hfm = new HorizontalFieldManager[row];
for (int i=0;i<row;i++) hfm[i] = new HorizontalFieldManager(Field.USE_ALL_WIDTH);
vfm = new VerticalFieldManager[row];
for (int i=0;i<row;i++) vfm[i] = new VerticalFieldManager(Field.USE_ALL_WIDTH);
}
public void add(int row, int col, Field obj) {
switch(col) {
case 1:
hfm[row-1].add(obj);
break;
case 2:
vfm[row-1].add(obj);
}
}
public void draw(boolean addLines) {
for (int i=0;i<this.row;i++) {
hfm[i].add(vfm[i]);
}
for (int i=0;i<this.row;i++) {
screen.add(hfm[i]);
if (addLines)
screen.add(new SeparatorField());
}
}
}
TimeUpdater.java：
package com.galaxy.dennis;
import java.util.Date;
import net.rim.device.api.i18n.SimpleDateFormat;
import net.rim.device.api.ui.UiApplication;
import net.rim.device.api.ui.component.Dialog;
public class TimeUpdater extends Thread {
private String time = "0:00";
private int[][] days;
private Alarm[] alarm;
public TimeUpdater(Alarm[] alarms) {
this.alarm = alarms;
Date date = new Date();
SimpleDateFormat hours = new SimpleDateFormat("H");
SimpleDateFormat minutes = new SimpleDateFormat("mm");
String h = hours.format(date);
String m = minutes.format(date);
time = h + ":" + m;
}
public void run() {
UiApplication.getUiApplication().invokeLater(new Runnable() {
public void run() {
Date date = new Date();
SimpleDateFormat hours = new SimpleDateFormat("H");
SimpleDateFormat minutes = new SimpleDateFormat("mm");
String h = hours.format(date);
String m = minutes.format(date);
time = h + ":" + m;
for (int i=0;i<5;i++) {
if (alarm[i].getTime() == time) Dialog.alert("Alarm: " + alarm[i].getName() + "!");
}
}
}, time(30), true);
}
public String getTime() {
return time;
}
public long time(int s) {
return s*1000;
}
}
Alarm.java：包com.galaxy.dennis；
public class Alarm {
private String time;
private String song;
private String name;
private int[] days;
public Alarm(String t, String s, String n, int[] d) {
this.time = t;
this.song = s;
this.name = n;
this.days = d;
}
public void setTime(String str) {
this.time = str;
}
public void setSong(String str) {
this.song= str;
}
public void setName(String str) {
this.name = str;
}
public void setDays(int[] d) {
this.days = d;
}
public String getTime() {
return this.time;
}
public String getSong() {
return this.song;
}
public String getName() {
return this.name;
}
public int[] getDays() {
return this.days;
}
}
为什么我会收到此错误？
编辑：编译消息：
Packaging project SuperAlarms B:\Apps\Eclipse\plugins\net.rim.ejde.componentpack6.0.0_6.0.0.43\components\bin\rapc.exe
-convertpng -quiet codename=deliverables\Standard\6.0.0\SuperAlarms -sourceroot=B:\Programming\Java\BlackBerry\SuperAlarms\src;B:\Programming\Java\BlackBerry\SuperAlarms\res
-import=B:\Apps\Eclipse\plugins\net.rim.ejde.componentpack6.0.0_6.0.0.43\components\lib\net_rim_api.jar deliverables\Standard\6.0.0\SuperAlarms.rapc B:\Programming\Java\BlackBerry\SuperAlarms\bin
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\Alarm.java:9: Warning!: member data 'String song' not required in class: com.galaxy.dennis.Alarm
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\Alarm.java:9: Warning!: member data 'int[] days' not required in class: com.galaxy.dennis.Alarm
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\Alarm.java:17: Warning!: method 'com.galaxy.dennis.Alarm.setTime(String)' not invoked.
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\Alarm.java:21: Warning!: method 'com.galaxy.dennis.Alarm.setSong(String)' not invoked.
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\Alarm.java:25: Warning!: method 'com.galaxy.dennis.Alarm.setName(String)' not invoked.
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\Alarm.java:29: Warning!: method 'com.galaxy.dennis.Alarm.setDays(int[])' not invoked.
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\Alarm.java:37: Warning!: method 'com.galaxy.dennis.Alarm.getSong()' not invoked.
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\Alarm.java:45: Warning!: method 'com.galaxy.dennis.Alarm.getDays()' not invoked.
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\GridOrganizer.java:15: Warning!: member data 'int row' not required in class: com.galaxy.dennis.GridOrganizer
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\GridOrganizer.java:15: Warning!: member data 'MainScreen screen' not required in class: com.galaxy.dennis.GridOrganizer
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\GridOrganizer.java:26: Warning!: method 'com.galaxy.dennis.GridOrganizer.add(int,int,Field)' not invoked.
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\GridOrganizer.java:36: Warning!: method 'com.galaxy.dennis.GridOrganizer.draw(boolean)' not invoked.
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\SuperAlarmsMainScreen.java:35: Warning!: member data 'Alarm[] alarms' not required in class: com.galaxy.dennis.SuperAlarmsMainScreen
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\SuperAlarmsMainScreen.java:35: Warning!: member data 'GridOrganizer g' not required in class: com.galaxy.dennis.SuperAlarmsMainScreen
B:\Programming\Java\BlackBerry\SuperAlarms\src\com\galaxy\dennis\SuperAlarmsMainScreen.java:35: Warning!: member data 'Font fnt_main' not required in class: com.galaxy.dennis.SuperAlarmsMainScreen
Packaging project SuperAlarms succeeded (took 2.932 seconds)
这是我启动程序后发生的情况的图片：
