重置按钮 Dicetester 无法正常工作

Question

我需要为学校制作一个骰子机。该应用程序显示图形和掷出的数字的骰子，并将这些数字放入一个 int 数组中。重置按钮需要清除此数组并更新界面，但这似乎不起作用。

它给出了以下错误代码：线程异常 "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

问题是：您在 clearArray() 中用空对象重置了数组。相反，您必须清除它或至少创建一个像这样的新数组：

numbers = new int[6];

重置按钮 Dicetester 无法正常工作

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