有人能告诉我为什么我的程序没有运行吗？

Question

 import java.awt.*;
 import java.awt.event.*;
 import javax.swing.*;
 
 public class RecallStudy extends JFrame
        implements KeyListener, 
            ActionListener
 {
    
    //CREATION OF ELEMENTS
     JLabel recallLabel;
     JTextField enterText;
     String enterTex;
     JTextField recieveText;
     JPanel displayInfo;
     GridBagConstraints constraints = new GridBagConstraints();
     
     
     public static void main (String [] args) {
         //MAKING THE WINDOW
         JFrame frame = new JFrame("RecallStudy");
            frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
            frame.setSize(500, 500);
            frame.setLocation(200, 200);
            frame.setContentPane(new RecallStudy());
            frame.pack();
            frame.setVisible(true);
    
}
     //GRIDLAYOUT CONSTRUCTION
        public RecallStudy() {
            setLayout(new GridBagLayout());
            constraints.weightx = 3.0;
            constraints.weighty = 3.0;
            constraints.fill = GridBagConstraints.BOTH;
            int x, y; // for clarity
            constraints.gridheight = 2; // span two rows
            addGB(recieveText,   x =2, y = 1);
            constraints.gridheight = 2; // set it back
            addGB(enterText,   x = 0, y = 1);
            constraints.gridwidth = 1; // span two columns
            addGB(new JLabel("Recall"),  x = 1, y = 0);
            constraints.gridwidth = 2; // set it back
            addGB(new JLabel(""), x = 0, y = 0);
            constraints.gridwidth = 1;
            addGB(new JLabel(""), x = 2, y =0);
            constraints.gridwidth = 1;
            addGB(new JLabel(""), x = 2, y = 2);
            constraints.gridwidth = 1;
            addGB (new JLabel(""), x = 0, y =2);
            constraints.gridwidth = 1;
            
       //Set the proper restrictions on the listeners
            enterText.addKeyListener(this);
            recieveText.setEditable(false);
        }

          void addGB(Component component, int x, int y) {
            constraints.gridx = x;
            constraints.gridy = y;
            add(component, constraints);
          }
          public RecallStudy(String name) {
              super (name);
          }
      
          public void keyTyped(KeyEvent e) {
              displayInfo(e, "KEY TYPED: ");
          }
          
          /** Handle the key pressed event from the text field. */
          public void keyPressed(KeyEvent e) {
              displayInfo(e, "KEY PRESSED: ");
          }
          
          /** Handle the key released event from the text field. */
          public void keyReleased(KeyEvent e) {
              displayInfo(e, "KEY RELEASED: ");
          }
          
          /** Handle the button click. */
          public void actionPerformed(ActionEvent e) {
              //Clear the text components.
              enterText.setText("");
              recieveText.setText(enterTex);
              
              //Return the focus to the typing area.
              enterText.requestFocusInWindow();
          }
         private void displayInfo (KeyEvent e, String keyStatus) {
             
         }

}

由于某种原因，这段代码没有运行...我不明白为什么...有人可以解释一下吗？当我把它关闭时，我的代码没有任何错误，但是当我尝试运行它的第二次它不起作用。我很困惑我缺少哪些组件来让它运行。我知道我还没有完成 displayInfo 部分，但这似乎不是它无法运行的原因。我真的很困惑，我觉得我开始这段代码的方式与其他所有代码一样，但这个无法运行。

Answer 1

对于初学者：

JTextField recieveText; // declares the field, but does not create it!

应该是这样的：

JTextField recieveText = new JTextField("No NullPointerException!");

然后：

JFrame frame = new JFrame("RecallStudy");
// ..
frame.setContentPane(new RecallStudy());

应该是这样的：

JFrame frame = new RecallStudy();
// ..
frame.setTitle("RecallStudy");

但老实说，该代码充满了“错误”。看完教程的 Swing 轨迹后，最好还是扔掉重新开始。

但这似乎不是它无法运行的原因

始终复制/粘贴错误和异常输出！