Resetbutton Dicetester funktioniert nicht richtig

Question

Ich muss einen Dudeltester für die Schule machen. Die Anwendung zeigt eine Grafik und die Würfel der geworfenen Zahlen und setzt diese Zahlen in ein int-Array. Die Reset-Schaltfläche muss dieses Array löschen und die Schnittstelle aktualisieren, aber dies scheint nicht zu funktionieren.

Es gibt den folgenden Fehlercode: Exception in thread "AWT-Eventqueue-0" java.lang.NullPointerException

public class DiceModel extends Observable { 

private int[] numbers; 
private int totalThrows; 
private int currentThrow; 

private boolean diceEnabled; 
private boolean graphView; 

/** 
* Initialize dice model 
*/ 
public DiceModel() { 
    numbers = new int[6]; 
    currentThrow = 0; 
    diceEnabled = false; 
    graphView = true; 

} 

//addObserver(view); 
public void addObs(DiceView x){ 
    addObserver(x); 
} 
public void addObs(DiceGraphView x){ 
    addObserver(x); 
} 
public void addObs(DiceTableView x){ 
    addObserver(x); 
} 


/** 
* 
* @return last thrown number 
*/ 
public int getCurrentThrow() { 
    return currentThrow; 
} 

/** 
* notifyObservers, add number to array 
* @param x Number to add 
*/ 
public void addNumber(int x) { 
    totalThrows++; 
    currentThrow = x; 

    //zet het randomnummer in de arraylist 
    int i = numbers[x]; 
    numbers[x] = ++i; 

    setChanged(); 
    notifyObservers(); 
} 

public void clearArray(){ 
    numbers = null; 
    setChanged(); 
} 


/** 
* 
* @return the most thrown number 
*/ 
public int getMaxNumber() { 
    int x = 0; 
    for(int i = 0; i < 6; i++) 
     if(numbers[i] > x) 
      x = numbers[i]; 

    return x; 
} 

/** 
* 
* @param n 
* @return Number of thrown n 
*/ 
public int getNumber(int n) { 
    if(n >= 0 && n < 6) 
     return numbers[n]; 
    else 
     return 0; 
} 

/** 
* 
* @return total thrown numbers 
*/ 
public int getTotalThrows() { 
    return totalThrows; 
} 

/** 
* 
* @return average 
*/ 
public int getAverage() { 
    int x = 0; 
    for(int i = 0; i < 6; i++) 
     if(numbers[i] > 0) 
      x += numbers[i]*(i+1); 

    return x/totalThrows; 
} 

/** 
* 
* @return boolean diceEnabled 
*/ 
public boolean isDiceEnabled() { 
    return diceEnabled; 
} 

/** 
* Switch diceEnabled and notifyObservers 
*/ 
public void switchDiceEnabled() { 
    diceEnabled = !diceEnabled; 
    setChanged(); 
    notifyObservers(); 
} 

/** 
* 
* @return boolean graphView 
*/ 
public boolean isGraphView() { 
    return graphView; 
} 

/** 
* Switch frequency table and 
*/ 
public void switchView() { 
    graphView = !graphView; 
    setChanged(); 
    notifyObservers(); 
} 
} 

public class DiceView extends JPanel implements Observer { 
private DiceModel model; 
private DiceGraphView graphView; 
private DiceTableView tableView; 

private boolean isGraphView; 
private BorderLayout layout; 
private Panel panel; 

/** 
* Initialize dice view and add graphView 
* @param model Add dice model for mvc 
*/ 
DiceView(DiceModel model){ 
    this.model = model; 
    isGraphView = model.isGraphView(); 

    graphView = new DiceGraphView(model); 
    tableView = new DiceTableView(model); 
    model.addObs(graphView); 
    model.addObs(tableView); 


    setLayout(new BorderLayout()); 
    panel = new Panel(); 
    layout = new BorderLayout(); 
    panel.setLayout(layout); 

    panel.add(graphView,BorderLayout.CENTER); 

    add(panel, BorderLayout.CENTER); 

} 

/** 
* Check if view has changed from model 
* @param obs 
* @param x 
*/ 
public void update(Observable obs, Object x) 
{ 
    if(isGraphView != model.isGraphView()) { 
     isGraphView = model.isGraphView(); 
     switchView(); 
    } 
} 

/** 
* Removes views from panel and add graph or table view 
* Revalidate panel and repaint panel. 
*/ 
public void switchView() { 
    panel.removeAll(); 
    if(isGraphView) { 
     panel.add(graphView, BorderLayout.CENTER); 
    } else { 
     panel.add(tableView,BorderLayout.CENTER); 
    } 
    panel.revalidate(); 
    panel.repaint(); 
} 
} 

public class DiceControl extends JPanel implements ChangeListener,ActionListener { 
private JButton start; 
private JButton stop; 
private JButton showDice; 
private JButton switchView; 
private JButton reset; 
private JSlider delay; 
private JTextField speed; 
private DiceModel model; 
private DiceControl control; 
private Timer timer; 
private Random randomGenerator; 

private JLabel info; 

/** 
* Initialize dice control 
* @param model Add dice model for mvc 
*/ 
public DiceControl(DiceModel model) 
{ 
    this.model = model; 
    control = this; // timer needs control 
    randomGenerator = new Random(); //maak nieuwe random 


    //maak alle button's etc. 
    info = new JLabel("Total throws 0, average 0"); 
    start = new JButton("Start"); 
    stop = new JButton("Stop"); 
    reset = new JButton("Reset"); 
    showDice = new JButton("Show/hide dice"); 
    switchView = new JButton("Switch view"); 

    speed = new JTextField("500 ms"); 
    speed.setEditable(false); 
    speed.setColumns(5); 

    delay = new JSlider(JSlider.HORIZONTAL, 1, 40,25); 
    delay.addChangeListener(this); 


    setLayout(new GridBagLayout()); 
    GridBagConstraints gbc = new GridBagConstraints(); 
    gbc.insets = new Insets(5,5,5,5); //van alle kanten 5 van de kant. 


    gbc.weightx = 1.0; 
    gbc.weighty = 1.0; 


    gbc.gridx = 0; 
    gbc.gridy = 0; 


    add(start, gbc); 
    gbc.gridx++; //x as ++ anders overlappen de buttons. 
    add(stop, gbc); 
    gbc.gridx++; 
    add(reset, gbc); 
    gbc.gridx++; 
    add(showDice, gbc); 
    gbc.gridx++; 
    add(switchView, gbc); 


    gbc.gridx = 0; 
    gbc.gridy++; 
    gbc.gridwidth = 4; 


    gbc.fill = GridBagConstraints.HORIZONTAL; 

    Panel panel = new Panel(); 
    panel.setLayout(new BorderLayout()); 

    panel.add(delay, BorderLayout.CENTER); 
    panel.add(speed, BorderLayout.EAST); 
    add(panel, gbc); 

    gbc.gridy++; 
    gbc.gridx=3; 
    gbc.gridwidth=1; 

    add(info,gbc); 


    //connect de objecten met de button dmv addActionListener() method. 
    start.addActionListener(new Start()); 
    stop.addActionListener(new Stop()); 
    reset.addActionListener(new Reset()); 
    showDice.addActionListener(new SwitchDice()); 
    switchView.addActionListener(new SwitchView()); 

} 

/** 
* Slicer value has changed 
* @param e 
*/ 
public void stateChanged(ChangeEvent e) { 
    //als de slider value verandert is verander de snelheid weergegeven op het label 
    speed.setText((delay.getValue()*50)+" ms"); //maal 50 want jslider loopt van 1-40 
} 

public void update() 
{ 
    //update de info 
    info.setText("Total throws "+model.getTotalThrows()+", average "+model.getAverage()); 
} 

/** 
* Timer has triggered event 
* add random number to model 
* @param event 
*/ 
public void actionPerformed(ActionEvent event) 
{ 
    int randomInt = randomGenerator.nextInt(6); //tussen de 0 inc en 6 ex 
    model.addNumber(randomInt); 
    //add het nummer in de arraylist in de class DiceModel 

    update(); 
    System.out.println(randomInt+1); 
} 

class Start implements ActionListener 
{ 
    public void actionPerformed(ActionEvent event) { 

     if (timer == null || !timer.isRunning()) 
     { 
      timer = new Timer(delay.getValue() * 50, control); 
      timer.start(); 
     } 
     start.setEnabled(false); 
     stop.setEnabled(true); 
    } 
} 

class Stop implements ActionListener 
{ 
    public void actionPerformed(ActionEvent event) 
    { 
     if(timer != null && timer.isRunning()) { 
      timer.stop(); 
     } 
     start.setEnabled(true); 
     stop.setEnabled(false); 
    } 
} 

class Reset implements ActionListener 
{ 
    public void actionPerformed(ActionEvent event) 
    { 
     timer.stop(); 
     model.clearArray(); 
     start.setEnabled(true); 
     stop.setEnabled(false); 
    } 
} 

class SwitchDice implements ActionListener 
{ 
    public void actionPerformed(ActionEvent event){ 
     model.switchDiceEnabled(); 
    } 
} 
class SwitchView implements ActionListener 
{ 
    public void actionPerformed(ActionEvent event) { model.switchView(); } 
} 


} 

Answer 1

Das Problem ist: Sie setzen Ihr Array in clearArray() mit einem Null-Objekt . Stattdessen haben Sie es zu löschen oder zumindest ein neues Array mit so etwas wie dies zu erstellen: [? Was für eine Nullpointer ist, und wie kann ich es beheben]

numbers = new int[6];