上周我们刚刚介绍了GUI和现在的Threads。我们得到了一个赋值，我们需要创建一个面板，通过Text Fields从用户收集upperBound，lowerBound，incrementValue和delayBetweenEachCount。该面板需要包含“开始”，“暂停”和“继续”按钮，允许用户完全控制程序，因为它通过incrementValue从具有delayBetweenEachCount的incrementBound计数从lowerBound到upperBound。
我刚刚开始研究它并且非常困惑，如果代码相当愚蠢我会道歉。
我不知道如何阅读错误消息。如果有人能突出我出错的一些方面，我将不胜感激。很感谢任何形式的帮助。提前谢谢。
尝试运行代码时收到以下错误消息：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at assignment5.CounterPanel.<init>(CounterPanel.java:139)
at assignment5.CounterPanel$2.run(CounterPanel.java:119)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
这是我目前的不完整代码：
public class CounterPanel extends javax.swing.JFrame {
// Creates new form
public CounterPanel() {
initComponents();
}
//Thread counter = new Thread(new Counter(lower, upper, valueIncrement, timeDelay));
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
lowerBoundLabel = new javax.swing.JLabel();
upperBoundLabel = new javax.swing.JLabel();
lowerBoundTextField = new javax.swing.JTextField();
upperBoundTextField = new javax.swing.JTextField();
incrementValueLabel = new javax.swing.JLabel();
delayValueLabel = new javax.swing.JLabel();
incrementValueTextField = new javax.swing.JTextField();
delayValueTextField = new javax.swing.JTextField();
startButton = new javax.swing.JButton();
pauseButton = new javax.swing.JButton();
continueButton = new javax.swing.JButton();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
setTitle("Counter");
lowerBoundLabel.setText("Lower bound:");
lowerBoundLabel.setName(""); // NOI18N
upperBoundLabel.setText("Upper bound: ");
incrementValueLabel.setText("Increment value:");
delayValueLabel.setText("Delay value: ");
startButton.setText("Start");
startButton.setName(""); // NOI18N
startButton.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
startButtonActionPerformed(evt);
}
});
pauseButton.setText("Pause");
continueButton.setText("Continue");
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(incrementValueLabel)
.addComponent(upperBoundLabel)
.addComponent(lowerBoundLabel)
.addComponent(delayValueLabel))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
.addComponent(incrementValueTextField, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, 27, Short.MAX_VALUE)
.addComponent(upperBoundTextField, javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(lowerBoundTextField)
.addComponent(delayValueTextField))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 135, Short.MAX_VALUE)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(continueButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(pauseButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(startButton, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
.addGap(15, 15, 15))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(55, 55, 55)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(lowerBoundTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(lowerBoundLabel, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
.addGap(18, 18, 18)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(upperBoundLabel)
.addComponent(upperBoundTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(18, 18, 18)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(incrementValueLabel)
.addComponent(incrementValueTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addGroup(layout.createSequentialGroup()
.addGap(65, 65, 65)
.addComponent(startButton)
.addGap(26, 26, 26)
.addComponent(pauseButton)))
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(18, 18, 18)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(delayValueLabel)
.addComponent(delayValueTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addGroup(layout.createSequentialGroup()
.addGap(5, 5, 5)
.addComponent(continueButton)))
.addContainerGap(87, Short.MAX_VALUE))
);
pack();
}// </editor-fold>
private void startButtonActionPerformed(java.awt.event.ActionEvent evt) {
counter.start();
}
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new CounterPanel().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JButton continueButton;
private javax.swing.JLabel delayValueLabel;
private javax.swing.JTextField delayValueTextField;
private javax.swing.JLabel incrementValueLabel;
private javax.swing.JTextField incrementValueTextField;
private javax.swing.JLabel lowerBoundLabel;
private javax.swing.JTextField lowerBoundTextField;
private javax.swing.JButton pauseButton;
private javax.swing.JButton startButton;
private javax.swing.JLabel upperBoundLabel;
private javax.swing.JTextField upperBoundTextField;
// End of variables declaration
int upper = Integer.parseInt(upperBoundTextField.getText());
int lower = Integer.parseInt(lowerBoundTextField.getText());
int valueIncrement = Integer.parseInt(incrementValueTextField.getText());
int timeDelay = Integer.parseInt(delayValueTextField.getText());
Thread counter = new Thread(new Counter(lower, upper, valueIncrement, timeDelay));
}
public class Counter implements Runnable{
int start;
int end;
int delayTime;
int incrementValue;
int i;
public Counter(int lower, int upper, int timeDelay, int valueIncrement){
start = lower;
end = upper;
delayTime = timeDelay;
incrementValue = valueIncrement;
i = lower;
}
public void run(){
try{
while(i <= end)
Thread.sleep(delayTime);
System.out.print(i);
i += incrementValue;
}catch(Exception e){}
}
}
答案 0 :(得分：1)
创建CounterPanel时，会创建Counter。但是Counter扩展了CounterPanel。因此，构建CounterPanel会创建一个Counter，创建一个Counter，创建一个Counter，创建一个Counter，...
Counter绝对没有理由延长CounterPanel。