您好，我试图在Jswing的方法中实际使用事件处理程序，当事件被触发时，我在线程中得到错误异常＆＃34; AWT-EventQueue-0＆＃ 34; java.lang.NullPointerException。我已经包含了GUI类，因此您可以了解发生了什么。问题在于方法setPlayerNameScreen及其中的事件处理程序。使用eclipse。
通常我的googlefu非常强大，因为这是我第一次在任何网站上发帖寻求帮助！任何帮助都是非常受欢迎的，因为我无法继续，直到我解决这个哈哈。
编辑：应该已经实际解释了代码的作用。当从前一个事件调用事件setPlayerNameScreen时，我们检查我们当前的玩家数量是否小于最大玩家数量，如果是，则将玩家名称更改为文本字段中的任何内容，将第1组添加到当前玩家计数并重置文本字段。
//Main game GUI class
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.math.*;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import java.awt.FlowLayout;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import javax.swing.JButton;
import javax.swing.JTextField;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class GameGUI extends JFrame
{
private JPanel startPanel;
private JPanel playerNamePanel;
private JTextField txtPlayerNumber;
GameManager gameMngr;
private int currentPlayer;
/**
* Launch the application.
*/
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
try
{
GameGUI frame = new GameGUI();
frame.setVisible(true);
}
catch (Exception e)
{
e.printStackTrace();
}
}
});
}
/**
* Create the frame.
*/
public GameGUI()
{
//Setup our game manager object
GameManager gameMngr = new GameManager();
//int for tracking current active player
int currentPlayer = 1;
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setBounds(100, 100, 450, 300);
startPanel = new JPanel();
startPanel.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(startPanel);
startPanel.setLayout(null);
JLabel lblTitle = new JLabel("Who Wants To Be a Zillionaire!");
lblTitle.setBounds(5, 5, 424, 14);
lblTitle.setHorizontalAlignment(SwingConstants.CENTER);
startPanel.add(lblTitle);
JLabel lblPlayerNumber = new JLabel("Please Enter How Many Players (max 4)");
lblPlayerNumber.setBounds(99, 55, 243, 92);
lblPlayerNumber.setHorizontalAlignment(SwingConstants.CENTER);
startPanel.add(lblPlayerNumber);
txtPlayerNumber = new JTextField();
txtPlayerNumber.setHorizontalAlignment(SwingConstants.CENTER);
txtPlayerNumber.setBounds(116, 153, 200, 20);
startPanel.add(txtPlayerNumber);
txtPlayerNumber.setColumns(10);
//action listener for game start screen button
JButton btnStart = new JButton("Start!");
btnStart.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent arg0)
{
//button has been pressed so pass player count and prepare for player names
int playerCount = Integer.valueOf(txtPlayerNumber.getText());
gameMngr.setPlayerCount(playerCount);
//set current panel invisible
startPanel.setEnabled(false);
startPanel.setVisible(false);
setPlayerNameScreen();
}
});
btnStart.setBounds(171, 200, 89, 23);
startPanel.add(btnStart);
}
private void setPlayerNameScreen()
{
//setup the player name setting panel
playerNamePanel = new JPanel();
playerNamePanel.setBorder(new EmptyBorder(5, 5, 5, 5));
setContentPane(playerNamePanel);
playerNamePanel.setLayout(null);
JLabel lblPlayerName = new JLabel("Player 1 Enter Your Name");
lblPlayerName.setHorizontalAlignment(SwingConstants.CENTER);
lblPlayerName.setBounds(87, 11, 259, 14);
playerNamePanel.add(lblPlayerName);
JTextField txtPlayerName = new JTextField();
txtPlayerName.setHorizontalAlignment(SwingConstants.CENTER);
txtPlayerName.setBounds(172, 81, 86, 20);
playerNamePanel.add(txtPlayerName);
txtPlayerName.setColumns(10);
JButton btnPlayerNameConf = new JButton("OK");
btnPlayerNameConf.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
if(currentPlayer <= gameMngr.getPlayerCount())
{
gameMngr.addPlayer(txtPlayerName.getText(), currentPlayer);
currentPlayer++;
txtPlayerName.setText("");
lblPlayerName.setText("Player " + currentPlayer + " Enter Your Name");
}
}
});
btnPlayerNameConf.setBounds(172, 142, 89, 23);
playerNamePanel.add(btnPlayerNameConf);
}
}
Edit2：完整错误
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at GameGUI$3.actionPerformed(GameGUI.java:132)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
答案 0 :(得分：2)
有问题的陈述如下GameGUI：
GameManager gameMngr = new GameManager();
在这里，您正在创建一个仅从该构造函数可见的局部变量。它与字段 gameMngr不同，我认为您应该写这些字段。通过将分配更改为简单来执行此操作：
gameMngr = new GameManager();
当然，setPlayerNameScreen()中的动作侦听器无法从构造函数访问局部变量，因此Java假设您指的是从未赋值的字段（null - 因此{{ 1}}）。