线程"main"中的JAVA异常java.lang.NullPointerException Sevens Dice Game

Question

我正在编写一个模拟骰子游戏'Sevens'的Java GUI.

我已经编写了用于创建GUI的主要部分.

我还没有编写程序的实际部分来实际玩游戏.

一切都正确编译,但我收到运行时错误:

Exception in thread "main" java.lang.NullPointerException
    at java.awt.Container.addImpl(Unknown Source)
    at java.awt.Container.add(Unknown Source)
    at SevensGameGUI.,init.(SevensGameGUI.java:88)
    at SeventsApplication.main(SevensApplication.java:13)

我不确定导致错误的原因是什么？

以下是SevensGameGUI.java的代码:

//include these import statements in every GUI class
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class SevensGameGUI extends JFrame {

     //Instance Variables
     // declares an array of integers to store the total score for each player
     // allocates memory for 5 players
      int[] totalScoreArray = new int[4];

      //declares an array of integers to store numbers rolled each time someone rolls the dice
      //allocates memory for at least 3 rolls
      int[] diceRollArray= new int[2];

      //declare an integer amount for the number of dice being rolled in the current turn
      int diceCount;

      //declare an integer to keep track of track of who the current player is
      int playerNumber;

      //declare a constant for the maximum throws allowed (three)
      public static final int MAX_THROWS = 3; 

      //declare an integer to remember how many times the first player rolled the dice
     int firstPlayerRolls;

     //declare an integer to keep count of the current player's rolls
     int currentPlayerRolls;

     //declare an integer to keep track of who is currently winning
     int winningPlayer;

     //declare all necessary GUI-related variables
     //JButtons:
     private JButton rollDiceButton;
     private JButton totalScoreButton;
     private JButton endTurnButton;

     //JLabels:
     private JLabel displayCurrentPlayerLabel;
     private JLabel displayFirstPlayerRollsLabel;
     private JLabel displayTotalScoreLabel;

     //JTextAreas:
     private JTextArea outputCurrentPlayerTextArea;
     private JTextArea outputFirstPlayerRollsTextArea;
     private JTextArea outputTotalScoreTextArea;
     private JTextArea outputDiceRollTextArea;
     private JTextArea outputTextArea;

     //JPanels:
     private JPanel labelPanel;
     private JPanel buttonPanel;


     //Declare an event-listener object of type SevensGameListener
     SevensGameListener listener;

//--------------------------------------------------------------------------------------------- 

//CONSTRUCTOR
public SevensGameGUI() {
super("Sevens Dice Game");

    //Initialize Buttons:
    rollDiceButton = new JButton("Roll Dice");
    totalScoreButton = new JButton("Total Your Score");
    endTurnButton = new JButton("End Turn");

    //Initialize Labels:
    displayCurrentPlayerLabel = new JLabel("Current Player: ");
    displayFirstPlayerRollsLabel = new JLabel("First player only rolled: ");
    displayTotalScoreLabel = new JLabel("Total Score: ");

    //Initialize Panels:
    labelPanel = new JPanel();
    labelPanel.setLayout(new GridLayout(3,2));
    labelPanel.add(displayCurrentPlayerLabel);
    labelPanel.add(outputCurrentPlayerTextArea);
    labelPanel.add(displayFirstPlayerRollsLabel);
    labelPanel.add(outputFirstPlayerRollsTextArea);
    labelPanel.add(displayTotalScoreLabel);
    labelPanel.add(outputTotalScoreTextArea);

    buttonPanel = new JPanel();
    buttonPanel.setLayout(new GridLayout(1,3));
    buttonPanel.add(rollDiceButton);
    buttonPanel.add(totalScoreButton);
    buttonPanel.add(endTurnButton);

    //Set The Layout as Border Layout
    this.setLayout(new BorderLayout());
    this.add(labelPanel, BorderLayout.NORTH);
    this.add(outputTextArea, BorderLayout.CENTER);
    this.add(buttonPanel, BorderLayout.SOUTH);

    //initilize/register Listener
    listener = new SevensGameListener();

    rollDiceButton.addActionListener(listener);
    totalScoreButton.addActionListener(listener);
    endTurnButton.addActionListener(listener);

    this.addWindowListener(listener);   

}//end of constructor

//---------------------------------------------------------------------------------------------

private class SevensGameListener implements ActionListener, WindowListener {

public void actionPerformed(ActionEvent ae) {

    if (ae.getSource() == rollDiceButton) {

    }
    if (ae.getSource() == totalScoreButton) {

    }
    if (ae.getSource() == endTurnButton) {
        playerNumber += 1;
    }


    outputTextArea.append(" ");         

}//end of method actionPerformed

public void windowClosing(WindowEvent we) {

     System.exit(0);            

}//end of windowClosing

public void windowDeactivated(WindowEvent we) { }
public void windowActivated(WindowEvent we) { }
public void windowClosed(WindowEvent we) { }
public void windowDeiconified(WindowEvent we) { }
public void windowIconified(WindowEvent we) { }
public void windowOpened(WindowEvent we) {  }



}//end of class CalculatorListener


}// end of SevensGameGUI class

而实际运行该程序的Application Class是

public class SevensApplication {

    public static void main (String[] args) {

        SevensGameGUI gui = new SevensGameGUI();
        gui.pack();
        gui.setVisible(true);

    }

}

我不确定我是否还没有完成部分GUI部分来实际运行游戏或者我的代码中是否有错误？即使我还没有在那里玩游戏的代码,它是否会影响我制作的gui的显示？

Answer 1

你还没有初始化任何一个TextArea.

喜欢和检查别人.

labelPanel.add(outputCurrentPlayerTextArea);

像这样初始化.

outputCurrentPlayerTextArea = new TextArea("Hello", 5, 40);

也为别人做TextArea.