Java错误：IllegalArgumentException：向容器添加窗口
我一直收到错误：
Exception in thread "main" java.lang.IllegalArgumentException: adding a window to a container at java.awt.Container.checkNotAWindow(Container.java:483) at java.awt.Container.addImpl(Container.java:1084) at java.awt.Container.add(Container.java:966) at Lab2.EmployeeGUI.main(EmployeeGUI.java:28) 有人可以帮助我，告诉我我做错了什么吗？ 我是初学者程序员。
package Lab2; import java.awt.*; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import javax.swing.*; /** * * @author Jim Doyle */ public class EmployeeGUI extends JFrame implements ActionListener { JTextField fName, mName, lName, phone, sal, years; JComboBox boxTitle, boxDept; DefaultListModel lstdefault; JList project; DbWork dbw = new DbWork("Lab2"); DbWork Title = new DbWork("Lab2"); DbWork Dept = new DbWork("Lab2"); DbWork Prjs = new DbWork("Lab2"); DbWork PrjList = new DbWork("Lab2"); public static void main(String[] args) { EmployeeGUI app = new EmployeeGUI(); JFrame frame = new JFrame("Employee Interface by Jim Doyle"); frame.getContentPane().add(app, BorderLayout.CENTER); frame.setSize(300, 300); frame.setVisible(true); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } public EmployeeGUI() { JPanel labels = new JPanel(); labels.setLayout(new GridLayout(8,1)); labels.add(new JLabel("First Name")); labels.add(new JLabel("MI")); labels.add(new JLabel("Last Name")); labels.add(new JLabel("Title")); labels.add(new JLabel("Telephone")); labels.add(new JLabel("Salary")); labels.add(new JLabel("Department")); labels.add(new JLabel("Years in Service")); getContentPane().add(labels, BorderLayout.WEST); JPanel fields = new JPanel(); fields.setLayout(new GridLayout(8,1)); fName = new JTextField(15); mName = new JTextField(15); lName = new JTextField(15); phone = new JTextField(15); sal = new JTextField(15); years = new JTextField(15); boxTitle = new JComboBox(); boxDept = new JComboBox(); fields.add(fName); fields.add(mName); fields.add(lName); fields.add(boxTitle); fields.add(phone); fields.add(sal); fields.add(years); getContentPane().add(fields, BorderLayout.CENTER); JPanel prjinfo = new JPanel(); prjinfo.setLayout(new GridLayout(1,2)); prjinfo.add(new JLabel("Project Description")); project = new JList(); lstdefault = new DefaultListModel(); // add items to title combo box while(Title.nextRecord()) { String txtTit = Title.getField(1); if(txtTit!=null) { boxTitle.addItem(Title.getField(1)); } } // add items to department combo box while(Dept.nextRecord()) { String txtDept = Dept.getField(2); if(txtDept!=null) { boxDept.addItem(Dept.getField(2)); } } while(PrjList.nextRecord()) { lstdefault.addElement(PrjList.getField(1)); } project = new JList(lstdefault); project.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); prjinfo.add(project); getContentPane().add(prjinfo, BorderLayout.SOUTH); } public void actionPerformed(ActionEvent e) { String button = e.getActionCommand(); if(button == "First") { if(dbw.firstRecord()) { Execute(); } } else if(button == "Next") { if(dbw.nextRecord()) { Execute(); } } else if(button == "Save") { String sql = "UPDATE FirstName, MiddleName, LastName, WorkPhone, Salary, YearsInService FROM Employee;"; dbw.processQuery(sql); } } private void action() { boxTitle.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { JComboBox b = (JComboBox)e.getSource(); String ntitle = (String)b.getSelectedItem(); updateTitle(ntitle); } }); } private void Execute() { fName.setText(dbw.getField(1)); mName.setText(dbw.getField(2)); lName.setText(dbw.getField(3)); phone.setText(dbw.getField(5)); sal.setText(dbw.getField(6)); years.setText(dbw.getField(8)); String ftext = dbw.getField(4); int dx = TitleList(ftext); boxTitle.setSelectedIndex(dx); String dtext = dbw.getField(7); int dx2 = DeptList(dtext); boxDept.setSelectedIndex(dx2); action(); } int TitleList(String title) { int dx = 0; for(int z=0; z<boxTitle.getItemCount(); z++) { if(title.equals(boxTitle.getItemAt(z))) { dx = z; } } return dx; } int DeptList(String dept) { int dx = 0; for(int z=0; z<boxDept.getItemCount(); z++) { if(dept.equals(boxDept.getItemAt(z))) { dx = z; } } return dx; } private void updateTitle(String title) { } }
EmployeeGUI从JFrame扩展，但在您的main方法中，您正在创建一个新的JFrame并尝试向其添加EmployeeGUI的实例。
更改EmployeeGUI ，使其从JPanel扩展
这里：
frame.getContentPane().add(app, BorderLayout.CENTER);
你试图将一个JFrame添加到一个没有意义的JFrame。
为什么不尝试显示应用程序而不是将其添加到JFrame。 或者甚至更好，没有EmployeeGUI扩展JFrame。
您无法将JFrame添加到另一个JFrame。 但是您可以将JPanel添加到JFrame，换句话说，更改EmployeeGUI以使其扩展为JPanel。