Java 非常烦人的AWT-EventQueue-0 NullPointerException。（几乎固定了。）
一直在四处研究，寻找许多答案，但没有运气Java 非常烦人的AWT-EventQueue-0 NullPointerException。（几乎固定了。）,java,swing,nullpointerexception,actionlistener,Java,Swing,Nullpointerexception,Actionlistener,一直在四处研究，寻找许多答案，但没有运气 public class GUIinput extends JFrame{ //Num is the JTextfield variable used for later. public JTextField num; public JButton button; public void test(){ //JPanel JPanel panel = new JPanel(); //Welcome JLabel
public class GUIinput extends JFrame{
//Num is the JTextfield variable used for later.
public JTextField num;
public JButton button;
public void test(){
//JPanel
JPanel panel = new JPanel();
//Welcome JLabel..Contains the welcome message.
JLabel welcome = new JLabel("Welcome to my Grade Calculator program!");
panel.add(welcome);
//Instructions J Label on how to work the program.
JLabel instructions = new JLabel("Enter your Mark and Weight to find your average grade!");
panel.add(instructions);
//JLabel---How many different assignments do the user want to evaluate?
JLabel number = new JLabel("<html><br>Firstly, please enter how many assignments/exams you want to evaluate?</html>");
panel.add(number);
//JTextField assigner.
num = new JTextField(18);
panel.add(num);
//Enter button
button = new JButton("Enter");
panel.add(button);
//JFrame maker.
setTitle("Grade Calculator");
setSize(575,250);
setVisible(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
add(panel);
//This action listener opens the new class Gradeanalysis(). The next window.
button.addActionListener(new Gradeanalysis());
//Action listener for the Textfield in case the user presses the enter key.
num.addActionListener(new Gradeanalysis());
}
public static void main(String[] args) {
new GUIinput().test();
}
}
我不知道该怎么做。感谢您的帮助，谢谢。您的问题在于：
//This action listener opens the new class Gradeanalysis(). The next window.
button.addActionListener(new Gradeanalysis());
//Action listener for the Textfield in case the user presses the enter key.
num.addActionListener(new Gradeanalysis());
ActionListener listener = new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
int messageType = JOptionPane.PLAIN_MESSAGE;
JOptionPane.showMessageDialog(null, num.getText(), "fasfa", messageType);
JFrame frame = new JFrame("Grade Calculator");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new JPanel());//dont have create main panel method
frame.pack();
frame.setVisible(true);
}
};
button.addActionListener(listener);
num.addActionListener(listener);
你的问题在于：
//This action listener opens the new class Gradeanalysis(). The next window.
button.addActionListener(new Gradeanalysis());
//Action listener for the Textfield in case the user presses the enter key.
num.addActionListener(new Gradeanalysis());
ActionListener listener = new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
int messageType = JOptionPane.PLAIN_MESSAGE;
JOptionPane.showMessageDialog(null, num.getText(), "fasfa", messageType);
JFrame frame = new JFrame("Grade Calculator");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(new JPanel());//dont have create main panel method
frame.pack();
frame.setVisible(true);
}
};
button.addActionListener(listener);
num.addActionListener(listener);
从给定的代码中，不清楚
GradeanalysisnumnumGradeanalysispublic class Gradeanalysis extends GUIinput implements ActionListener{
JTextField num;
public Gradeanalysis(JTextField num)
{
this.num = num;
}
//Implement the actionPerformed here as u have..
}
Gradeanalysisbutton.addActionListener(new Gradeanalysis(num));
现在我将注意到，所执行的操作可能不会像您预期的那样对TextField起作用，并且a、make the others JDialogs或其他东西。从给定的代码中，不清楚
GradeanalysisnumnumGradeanalysispublic class Gradeanalysis extends GUIinput implements ActionListener{
JTextField num;
public Gradeanalysis(JTextField num)
{
this.num = num;
}
//Implement the actionPerformed here as u have..
}
Gradeanalysisbutton.addActionListener(new Gradeanalysis(num));
现在我将注意到，执行的操作可能不会像您期望的那样对TextField起作用，并且a，使其他JDialogs或其他东西成为新的类。仅为指针创建一个新类？所以现在应该是button.addActionListener（newclassname（））；我认为更好的解决方案是在将操作侦听器添加到组件之前，将其分配给变量或字段。添加了一个匿名内部类的示例，该示例应该可以工作，尽管如果它是separateThans，则会更好，但这将不适用于我的程序。我要做的是从GUIinput类获取输入，并将其作为Gradeanalysis类中的变量。我假设您的代码只在GUIinput类中完成上述所有操作。这将是一个问题，因为在GUI输入中执行的任何操作都会改变GradeAnaylis类的外观。是否只为指针创建一个新类？所以现在应该是button.addActionListener（newclassname（））；我认为更好的解决方案是在将操作侦听器添加到组件之前，将其分配给变量或字段。添加了一个匿名内部类的示例，该示例应该可以工作，尽管如果它是separateThans，则会更好，但这将不适用于我的程序。我要做的是从GUIinput类获取输入，并将其作为Gradeanalysis类中的变量。我假设您的代码只在GUIinput类中完成上述所有操作。这将是一个问题，因为在GUI输入中所做的任何事情都会改变GradeAnalysis类的外观。你知道
newGradeanalysisGUIinputJTextFieldJButtonJTextFieldJOptionPaneactionPerformed（…）GradeanalysisGUIinputJTextFieldJButtonJTextFieldJOpti中可见