如何使用一个继承MIDlet的抽象类
大家好！
现在发现一个抽象类继承MIDlet,但运行后，自动推出了，然后报错：java.lang.InstantiationException
想问下，MIDlet不是个抽象类吗？为什么还要写一个抽象类来继承它呢？
abstract public class SDAApplication extends MIDlet {
private static SDAApplication instance;
protected final SDAApplication Application = this;
private AppCanvas appCanvas = null;
private Graphics graphics = null;
private Display disp = Display.getDisplay(this);
private SDAForm foucsedForm = null;
private SDAForm mainForm = null;
public SDAInputPanel inputPanel = new SDAInputPanel();
private Vector dispList = new Vector();
private SDAMessageBox msgBox;
public static final int SKIN_STANDARD = 0;
public static final int SKIN_POPULAR = 1;
private SDASkins Skins = null;
private int skin = SKIN_STANDARD;
private boolean doubleBuffered = true;
private boolean ctrl3d = false;
private Timer runOneceTimer = new Timer();
public SDAApplication() {
instance = this;
this.appCanvas = new AppCanvas();
this.appCanvas.setFullScreenMode(true);
this.disp.setCurrent(appCanvas);
}
public final void setSkin(int skin) {
this.skin = skin;
if (skin == SKIN_POPULAR) {
Skins = null;
Skins = SDASkins.CreateSkins();
}
}
public final void setDoubleBuffered(boolean doubleBuffered) {
this.doubleBuffered = doubleBuffered;
}
public void setCtrl3d(boolean ctrl3d) {
this.ctrl3d = ctrl3d;
}
public void setMainForm(SDAForm mainForm) {
this.mainForm = mainForm;
}
public final boolean isDoubleBuffered() {
return this.doubleBuffered;
}
public final boolean hasPointer() {
return this.appCanvas.hasPointerEvents();
}
protected final Graphics GetGraphics() {
return this.graphics;
}
protected final Canvas GetCanvas() {
return this.appCanvas;
}
protected SDAForm getFoucsedForm() {
return foucsedForm;
}
public int getSkin() {
return skin;
}
public boolean isCtrl3d() {
return ctrl3d;
}
public static SDAApplication GetInstance() {
return instance;
}
public void MessageBox(String Caption, String Text, int flags) {
MessageBox(Caption, Text, flags, null);
}
public void MessageBox(String Caption, String Text, int flags,
MsgBoxCloseEvent closeEvent) {
msgBox.closeEvents.addElement(closeEvent);
msgBox.caption = Caption;
msgBox.txtLabel.setText(Text);
msgBox.button1.setVisible(false);
msgBox.button2.setVisible(false);
int btnFlags = flags % 10;
switch (btnFlags) {
case SDAConsts.MB_OK: {
msgBox.button1.setVisible(true);
msgBox.button1.setText("确定");
break;
}
case SDAConsts.MB_YESNO: {
msgBox.button1.setVisible(true);
msgBox.button2.setVisible(true);
msgBox.button1.setText("是");
msgBox.button2.setText("否");
break;
}
default: {
msgBox.button1.setVisible(true);
msgBox.button1.setText("确定");
break;
}
}
//System.out.println("MessageBoxEnd");
if (msgBox.button2.visible) {
msgBox.button2.setFoucsed();
} else if (msgBox.button1.visible) {
msgBox.button1.setFoucsed();
}
msgBox.InternalShow();
}
protected final void ShowForm(SDAForm form) {
int index = dispList.indexOf(form);
//System.out.println("ShowForm index=" + index);
if (index > -1) {
dispList.removeElementAt(index);
}
dispList.addElement(form);
foucsedForm = form;
form.canvas = this.appCanvas;
form.graphics = this.graphics;
disp.setCurrent(appCanvas);
form.Repaint();
}
protected final void CloseForm(SDAForm form) {
int index = dispList.indexOf(form);
if (index > -1) {
dispList.removeElementAt(index);
}
if (!dispList.isEmpty()) {
Object current = dispList.lastElement();
if (current instanceof SDAForm) {
((SDAForm) current).Show();
} else {
disp.setCurrent((Displayable) current);
}
}else
{
if(mainForm!=null&&!mainForm.equals(form))
{
mainForm.Show();
}
else
{
Application.Exit();
}
}
}
public final void ShowDisplayable(Displayable displayable) {
//System.out.println("ShowDisplayable");
int index = dispList.indexOf(displayable);
if (index > -1) {
dispList.removeElementAt(index);
}
dispList.addElement(displayable);
disp.setCurrent(displayable);
}
public final void CloseDisplayable(Displayable displayable) {
//System.out.println("CloseDisplayable");
int index = dispList.indexOf(displayable);
if (index > -1) {
//System.out.println("Remove displayable index=" + index);
dispList.removeElementAt(index);
}
if (!dispList.isEmpty()) {
Object current = dispList.lastElement();
if (current instanceof SDAForm) {
((SDAForm) current).Show();
} else {
disp.setCurrent((Displayable) current);
}
}
}
public void startApp() {
msgBox = new SDAMessageBox();
runOneceTimer.schedule(new TimerTask() {
public void run() {
while (graphics == null) {
appCanvas.repaint();
}
if (foucsedForm != null) {
//System.out.println("startApp");
foucsedForm.Show();
}
runOneceTimer.cancel();
}
}, 0, 10);
}
public void pauseApp() {
}
public void destroyApp(boolean unconditional) {
}
public final void Exit() {
this.quitApp();
}
public final void quitApp() {
this.foucsedForm = null;
this.appCanvas = null;
this.dispList.removeAllElements();
instance.destroyApp(true);
instance.notifyDestroyed();
instance = null;
}
class AppCanvas extends Canvas {
public void paint(Graphics g) {
//System.out.println("paint");
if (graphics == null) {
graphics = g;
return;
}
if (!instance.isDoubleBuffered() && foucsedForm != null) {
foucsedForm.graphics = g;
foucsedForm.paint();
}
}
protected void showNotify() {
//System.out.println("showNotify");
if (foucsedForm != null) {
foucsedForm.paint();
}
}
protected void pointerPressed(int x,
int y) {
if (foucsedForm != null) {
foucsedForm.pointerPressed(x, y);
}
}
protected void pointerReleased(int x,
int y) {
if (foucsedForm != null) {
foucsedForm.pointerReleased(x, y);
}
}
protected void pointerDragged(int x, int y) {
if (foucsedForm != null) {
foucsedForm.pointerDragged(x, y);
}
}
protected void keyPressed(int keyCode) {
//String keyName = getKeyName(keyCode).toUpperCase();
if (foucsedForm != null) {
foucsedForm.keyPressed(keyCode);
}
}
protected void keyReleased(int keyCode) {
if (foucsedForm != null) {
foucsedForm.keyReleased(keyCode);
}
}
}
[解决办法]
直接写个类的话少了点强制性了，
如果直接写个类有些人可能不知道哪几个方法必须实现的，
写抽象类的方法好处是只要方法是抽象的且是保护的，子类就得强制实现。。
