Java 数组中的NullPointerException
我有一个JFrame和JTextFields,它们从用户那里获取输入并添加到数组中 这是它的ActionListenerJava 数组中的NullPointerException,java,arrays,nullpointerexception,Java,Arrays,Nullpointerexception,我有一个JFrame和JTextFields,它们从用户那里获取输入并添加到数组中 这是它的ActionListener class ButtonHandlerSub implements ActionListener{ public void actionPerformed(ActionEvent ae){if(ae.getSource() == add2){ //add new student here Student temp
class ButtonHandlerSub implements ActionListener{
public void actionPerformed(ActionEvent ae){if(ae.getSource() == add2){
//add new student here
Student temp = new Student(Integer.parseInt(tId.getText()),tName.getText(),tCourse.getText(),
Integer.parseInt(tYear.getText()),tGender.getText());
sLogic.addStudentArray(temp); // this is line 168
addStud.dispose();
}
这是声明sLogic的contsructor
public StudentGUI() throws Exception{
ButtonHandler bh = new ButtonHandler();
//Instantiate Main frame buttons
add = new JButton("Add Student");
add.addActionListener(bh);
del = new JButton("Delete Student");
edit = new JButton("Edit Student");
edit.addActionListener(bh);
save = new JButton("Save Changes");
//Main frame buttons added to JPanel actions
actions = new JPanel(new GridBagLayout());
GridBagConstraints b = new GridBagConstraints();
b.insets = new Insets(5,0,5,0);
b.fill = GridBagConstraints.HORIZONTAL;
actions.add(add,b);
b.gridy = 1;
actions.add(del,b);
b.gridy = 2;
actions.add(edit,b);
b.gridy = 3;
actions.add(save,b);
sLogic = new StudentLogic();
model = new DefaultTableModel(sLogic.getStudentArray(),sLogic.getColumnLabel());
table = new JTable(model){
public boolean isCellEditable(int row,int col){
return false;
}
};
//add Jtable to scroller
JScrollPane scroller = new JScrollPane(table);
main = new JFrame("Student Database");
main.setLayout(new GridBagLayout());
GridBagConstraints a = new GridBagConstraints();
a.insets = new Insets(10,5,10,5);
main.add(scroller,a);
a.gridx=1;
a.weighty = 1;
main.add(actions,a);
main.pack();
main.setVisible(true);
main.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//set JButtons edit and del disabled as default
edit.setEnabled(false);
del.setEnabled(false);
}
下面是addStudentArray()方法
第168行是sLogic.addStudentArray(temp) 以下内容将暂时防止
螺柱中出现空值
public synchronized void addStudentArray(Student studArr){
Student[] enlargedStuds = Arrays.copyOf(studs, studs.length + 1);
enlargedStuds[enlargedStuds.length - 1] = studArr;
studs = enlargedStuds;
}
ButtonHandlerSub对象中的sLogic可能与StudentGUI中初始化的sLogic不同
这就是你写的:
public StudentGUI() throws Exception{
ButtonHandler bh = new ButtonHandler();
...
sLogic = new StudentLogic(); // <- this is not the bh.sLogic!
...
public StudentGUI()引发异常{
ButtonHandler bh=新ButtonHandler();
...
sLogic=new StudentLogic();//您应该发布控制台输出,以便所有人都知道哪一行发生异常,哪一行抛出NPE?NPE位于第168行,即sLogic.addStudentArray(temp);这意味着sLogic是空的。也许sLogic
是空的。你在哪里初始化它?我现在似乎得到了它。但是如果我在类中实例化它为private StudentLogic sLogic;
它不应该在类中可访问吗?我现在看不到层次结构。ButtonHandler类是在Stude中声明的吗ntGUI?ButtonHandler是否有sLogic变量?我将if语句从ButtonHandlerSub传输到ButtonHandler,现在似乎工作正常。谢谢先生!
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at StudentGUI$ButtonHandlerSub.actionPerformed(StudentGUI.java:168)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
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:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
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:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:703)
at java.awt.EventQueue.access$000(EventQueue.java:102)
at java.awt.EventQueue$3.run(EventQueue.java:662)
at java.awt.EventQueue$3.run(EventQueue.java:660)
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:676)
at java.awt.EventQueue$4.run(EventQueue.java:674)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:673)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)
public synchronized void addStudentArray(Student studArr){
Student[] enlargedStuds = Arrays.copyOf(studs, studs.length + 1);
enlargedStuds[enlargedStuds.length - 1] = studArr;
studs = enlargedStuds;
}
public StudentGUI() throws Exception{
ButtonHandler bh = new ButtonHandler();
...
sLogic = new StudentLogic(); // <- this is not the bh.sLogic!
...