我正在编写一个模拟骰子游戏“Sevens”的 Java GUI。
我已经编写了创建 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，但我得到一个运行时错误：
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)
我不确定是什么导致了错误？
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
而实际运行程序的应用程序类是
public class SevensApplication {
public static void main (String[] args) {
SevensGameGUI gui = new SevensGameGUI();
gui.pack();
gui.setVisible(true);
}
}
我不确定我是否刚刚完成了 GUI 部分的一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，它会影响我制作的 gui 的显示吗？