public class ControllerGui {
private JFrame frame;
private JTextField textField;
private JTextField textField_1;
private JTextField textField_2;
private JLabel lblStatuslabel;
public JLabel lblPortlabel;
public JLabel lblIplabel;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
ControllerGui window = new ControllerGui();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public ControllerGui() {
initialize();
}
/**
* Initialize the contents of the frame.
*/
public void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 450, 600);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
JTabbedPane tabbedPane = new JTabbedPane(JTabbedPane.TOP);
tabbedPane.setBorder(null);
tabbedPane.setBounds(6, 6, 438, 570);
frame.getContentPane().add(tabbedPane);
JPanel panel = new JPanel();
panel.setBorder(null);
tabbedPane.addTab("Connection", null, panel, null);
panel.setLayout(null);
JLabel lblTcpipConnection = new JLabel("TCP/IP Connection");
lblTcpipConnection.setBounds(6, 6, 91, 13);
lblTcpipConnection.setFont(new Font("Lucida Grande", Font.PLAIN, 10));
panel.add(lblTcpipConnection);
JLabel lblNewLabel = new JLabel("IP Address :");
lblNewLabel.setBounds(17, 24, 74, 16);
panel.add(lblNewLabel);
textField = new JTextField();
textField.setBounds(97, 18, 165, 28);
panel.add(textField);
textField.setColumns(10);
JButton btnNewButton = new JButton("Connect");
btnNewButton.addMouseListener(new MouseAdapter() {
@Override
public void mouseClicked(MouseEvent e) {
System.out.println("Clicked");
lblStatuslabel.setVisible(true);
}
});
btnNewButton.setBounds(268, 18, 151, 29);
panel.add(btnNewButton);
JLabel lblPort = new JLabel("Port :");
lblPort.setBounds(58, 58, 33, 16);
panel.add(lblPort);
textField_1 = new JTextField();
textField_1.setBounds(97, 52, 165, 28);
panel.add(textField_1);
textField_1.setColumns(10);
JButton btnDisconnect = new JButton("Disconnect");
btnDisconnect.setBounds(268, 52, 151, 29);
panel.add(btnDisconnect);
JLabel lblConnectionStatus = new JLabel("Connection Status");
lblConnectionStatus.setBounds(6, 86, 91, 12);
lblConnectionStatus.setFont(new Font("Lucida Grande", Font.PLAIN, 10));
panel.add(lblConnectionStatus);
JLabel lblStatus = new JLabel("Status");
lblStatus.setBounds(52, 103, 39, 16);
panel.add(lblStatus);
JLabel lblStatuslabel = new JLabel("CONNECTED!");
lblStatuslabel.setForeground(Color.GREEN);
lblStatuslabel.setVisible(false);
lblStatuslabel.setBounds(97, 103, 91, 16);
panel.add(lblStatuslabel);
JLabel lblNewLabel_1 = new JLabel("IP Status");
lblNewLabel_1.setBounds(37, 124, 54, 16);
panel.add(lblNewLabel_1);
JLabel lblIplabel = new JLabel("192.168.110.1");
lblIplabel.setVisible(false);
lblIplabel.setBounds(97, 124, 109, 16);
panel.add(lblIplabel);
JLabel lblPortStatus = new JLabel("Port Status");
lblPortStatus.setBounds(23, 145, 68, 16);
panel.add(lblPortStatus);
JLabel lblPortlabel = new JLabel("1234");
lblPortlabel.setVisible(false);
lblPortlabel.setBounds(97, 145, 83, 16);
panel.add(lblPortlabel);
JLabel lblLog = new JLabel("Log");
lblLog.setBounds(6, 166, 17, 13);
lblLog.setFont(new Font("Lucida Grande", Font.PLAIN, 10));
panel.add(lblLog);
JTextArea textArea = new JTextArea();
textArea.setBounds(6, 191, 401, 327);
panel.add(textArea);
JSeparator separator = new JSeparator();
separator.setBounds(100, 7, 315, 13);
panel.add(separator);
JSeparator separator_1 = new JSeparator();
separator_1.setBounds(100, 88, 80, 6);
panel.add(separator_1);
JSeparator separator_2 = new JSeparator();
separator_2.setBounds(25, 168, 390, 12);
panel.add(separator_2);
JLabel lblNewLabel_2 = new JLabel("Modbus ID");
lblNewLabel_2.setFont(new Font("Lucida Grande", Font.PLAIN, 10));
lblNewLabel_2.setBounds(204, 86, 54, 16);
panel.add(lblNewLabel_2);
JSeparator separator_3 = new JSeparator();
separator_3.setBounds(261, 88, 151, 12);
panel.add(separator_3);
JLabel lblSlaveId = new JLabel("ID :");
lblSlaveId.setBounds(204, 124, 33, 16);
panel.add(lblSlaveId);
textField_2 = new JTextField();
textField_2.setBounds(232, 118, 74, 28);
panel.add(textField_2);
textField_2.setColumns(10);
JButton btnNewButton_1 = new JButton("CONNECT");
btnNewButton_1.setBounds(316, 104, 91, 58);
panel.add(btnNewButton_1);
JPanel panel_1 = new JPanel();
tabbedPane.addTab("Controller", null, panel_1, null);
}
}
嗨！我正在努力实施 的mouseClicked（） 函数在我的代码中。如您所见，在初始化中，我设置了组件lblStatuslbl.setVisible（false）。然后，在public void mouseClicked（），当它被trigerred时，我设置为lblStatuslbl.setVisible（）为true。但是当我尝试它时，我得到了一些错误代码：
Clicked
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at ControllerGui$2.mouseClicked(ControllerGui.java:105)
at java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaster.java:270)
at java.awt.Component.processMouseEvent(Component.java:6519)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3320)
at java.awt.Component.processEvent(Component.java:6281)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4872)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4501)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4698)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:708)
at java.awt.EventQueue$4.run(EventQueue.java:706)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
有人可以帮我解决这个问题吗？非常感谢你！
答案 0 :(得分：2)
你通过在initialize方法中重新声明它来影响lblStatuslabel。这使得它在类中保持为null，因此当您调用lblStatuslabel.setVisible(true)时，您将抛出一个NPE：
public void mouseClicked(MouseEvent e) {
System.out.println("Clicked");
lblStatuslabel.setVisible(true); // ***** here *****
}
解决方案：不要遮蔽你的变量。所以不要这样：
public class Foo {
private String bar; // this variable stays null
public Foo() {
initialize();
}
public void intialize() {
// this initialize a *local* variable
String bar = "baz";
}
}
做的：
public class Foo {
private String bar;
public Foo() {
initialize();
}
public void intialize() {
bar = "baz"; // note the difference?
}
}
修改
更重要的是，为了获得长期利益，您需要了解如何调试NullPointerException（NPE）。您需要检查返回的堆栈跟踪，找到抛出NPE的行，并使用调试器或println语句仔细检查任何空变量的行，例如：
System.out.println("is lblStatuslabel null?: " + (lblStatuslabel == null));
然后搜索回代码，看为什么变量为null。你将一次又一次地遇到这些，相信我。
修改2
同样Dic19精明地提到，你不应该使用MouseListener来监听按钮按下，而是使用ActionListener或AbstractAction。后面这些人专门为按钮和菜单而构建，并且比MouseListener更好地使用它们。如果它们被禁用，则按钮被适当禁用 - 对于MouseListener不适用。适当的监听器将允许按钮与空格键按下 - 对于MouseListener不适用。适当的侦听器将actionCommand String传递给侦听器事件 - 对于MouseListener而言不是这样。
此外，您还希望避免使用null布局和setBounds(...)，因为这会导致创建一个严格的GUI，除了您自己的系统和屏幕分辨率外，它们看起来很糟糕，这很难维护，调试和增强。而是学习并使用布局管理器。