“线程中的异常”;AWT-EventQueue-0“;GUI中的java.lang.NullPointerException?
我是初学者,我使用JavaGUI,我不明白为什么会有错误。我有一个“线程中的异常”;AWT-EventQueue-0“;GUI中的java.lang.NullPointerException?,java,swing,nullpointerexception,Java,Swing,Nullpointerexception,我是初学者,我使用JavaGUI,我不明白为什么会有错误。我有一个class-Phong(它是Frameclass)和class-LoaiPhong。在Phong类中,当我尝试通过方法GetItem5()和GetPop()获取LoaiPhong类中的属性时,会出现错误。但是,label(MainPanel.add(phongThuong[0].GetLabel());)运行良好。那么,为什么我会得到错误 public class Phong extends javax.swing.JFrame
class-Phong
(它是Frameclass)和class-LoaiPhong
。在Phong
类中,当我尝试通过方法GetItem5()
和GetPop()
获取LoaiPhong
类中的属性时,会出现错误。但是,label(MainPanel.add(phongThuong[0].GetLabel());)
运行良好。那么,为什么我会得到错误
public class Phong extends javax.swing.JFrame {
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
phongThuong[0] = new LoaiPhong();
MainPanel.add(phongThuong[0].GetLabel());
phongThuong[0].GetItem5().addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
JOptionPane.showMessageDialog(null, "Time start:",
"Title", JOptionPane.WARNING_MESSAGE);
}
});
phongThuong[0].GetPop().add(phongThuong[0].GetItem5());
}
}
class LoaiPhong{
private JMenuItem item5;
private JPopupMenu pop;
LoaiPhong(){
JMenuItem item5 = new JMenuItem("Move");
}
JPopupMenu GetPop(){
return this.pop;
}
JMenuItem GetItem5(){
return this.item5;
}
}
error:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at doanjava3.Phong.jButton1ActionPerformed(Phong.java:160)
at doanjava3.Phong.access$000(Phong.java:32)
at doanjava3.Phong$1.actionPerformed(Phong.java:81)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6533)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6298)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
更新:
我试图更改
私有JMenuItem item5
;toprivate JMenuItem item5=新JMenuItem(“移动”)代码>和私有JPOppMenu pop
toprivate JPOPUPMENUS pop=new JPOPUPMENUS(“选项”)代码>而且运行良好,发生了什么事????我想在constructor中我已经初始化了JMenuItem item5=newjmenuitem(“Move”)代码>但为什么要在属性中初始化它?我将此回复到您的更新:
它运行得很好,因为您最初没有正确初始化变量。您刚才说的是private JMenuItem item5
,然后在构造函数中说的是JMenuItem item5=newjmenuitem(“移动”)
这是错误的,因为您需要从构造函数中删除JMenuItem
关键字,并且只允许item5=newjmenuitem(“移动”)代码>
尝试在类构造函数中初始化它们(好方法),而不是在构造函数外部初始化(坏方法)
还可以尝试在Phong
类中实现ActionListener
,并添加未实现的方法 此异常在哪一行引发?顺便说一句:请使用Java代码样式:函数名在Java中不以大写字符开头。我不明白为什么会出错。
-错误消息告诉您。第160行有一个包含空值的变量。所以首先找出哪个变量是空的,然后找出它为什么是空的。我们无能为力,因为我们不知道你的方法做什么。它运行得很好——因为你实际上将值初始化为非nullyes,我看到了,但是你需要从类构造函数中删除JMenuItem
关键字。每次,当你想初始化某个东西时,按照我在回答中说的那样做。试着比较一下我写的和你写的,你能看出有什么不同吗?
class Phong()
{
private JMenuItem item5
public Phong()
{
item5=new JMenuItem("Move");
}
}