我有一个带有JTextFields的JFrame，它从用户那里获取输入以添加到数组中。
这是它的ActionListener
class ButtonHandlerSub implements ActionListener{
public void actionPerformed(ActionEvent ae){if(ae.getSource() == add2){
//add new student here
Student temp = 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的构造器
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);
}
这是方法addStudentArray（）
public void addStudentArray(Student studArr){
studs = Arrays.<Student>copyOf(studs,studs.length+1);
studs[studs.length-1]=studArr;
}
在构造函数的类中：
public StudentLogic() throws Exception {
output = new ObjectOutputStream(new FileOutputStream("students_updated.dat"));
input = new ObjectInputStream(new FileInputStream("students.dat"));
studs = (Student[]) input.readObject();
studs2 = new Object[studs.length][5];
for(int i = 0; i < studs.length; i++){
studs2[i][0]=studs[i].getID()+"";
studs2[i][1]= studs[i].getName();
studs2[i][2]= studs[i].getCourse();
studs2[i][3]= studs[i].getYr();
studs2[i][4]= studs[i].getGender();
}
input.close();
}
我被这个异常困住了，我不知道为什么它返回npe。我很确定我已经宣布。如果需要，我可以发布更多代码。提前致谢 ：）
至于控制台
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)
第168行是sLogic.addStudentArray（temp）;
最佳答案
ButtonHandlerSub对象中的sLogic可能与StudentGUI中已初始化的sLogic不同。
这是你写的：
public StudentGUI() throws Exception{
ButtonHandler bh = new ButtonHandler();
...
sLogic = new StudentLogic(); // <- this is not the bh.sLogic!
...
关于java - 数组中的NullPointerException，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/11330182/