我有两个 JcomboBox（如图），items都是从MySQL拿的，分别是在 title 和 date 桌子。
我目前的code就是当 Select 的 comboBox item 选后，它才会 display date (Date JComboBox)。有什么方法可以让它一开始就自动display date 而不是要我选了Angry Birds 之后才 display date 吗 ？ 谢谢。
public class BuyTicket {
static JFrame frame;
JLabel title,lblMainDate,selectMovie,dateOfShow;
JComboBox Select,Date;
public JPanel createContentPane() throws IOException
{
Select = new JComboBox();
Select.setLocation(115,90);
Select.setSize(175, 20);
try {
DatabaseConnection db=new DatabaseConnection();
Connection connect=db.getConnection();
String sql="Select title FROM movie";
PreparedStatement ps=connect.prepareStatement(sql);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
String name = rs.getString("title");
Select.addItem(name);
}
} catch (Exception e) {
e.printStackTrace();
}
Select.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
JComboBox comboBox=(JComboBox) event.getSource();
Object selected = Select.getSelectedItem();
displayDate(selected);
}
});
}
private void displayDate(Object selected) {
// TODO Auto-generated method stub
try {
Date.removeAllItems();
DatabaseConnection db=new DatabaseConnection();
Connection connect=db.getConnection();
String sql="Select date FROM movie WHERE title = ?";
PreparedStatement ps=connect.prepareStatement(sql);
ps.setObject(1, selected);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
String date1 = rs.getString("date");
DefaultComboBoxModel model = (DefaultComboBoxModel)Date.getModel();
if (model.getIndexOf(date1) == -1)
{
Date.addItem(date1);
}
}
} catch (Exception e) {
System.out.println("null");
}
}
}
Edited
public class BuyTicket {
static JFrame frame;
JLabel title,lblMainDate,selectMovie,dateOfShow;
JComboBox Select,Date;
public JPanel createContentPane() throws IOException
{
Select = new JComboBox();
Select.setLocation(115,90);
Select.setSize(175, 20);
try {
DatabaseConnection db=new DatabaseConnection();
Connection connect=db.getConnection();
String sql="Select title FROM movie";
PreparedStatement ps=connect.prepareStatement(sql);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
String name = rs.getString("title");
Select.addItem(name);
}
} catch (Exception e) {
e.printStackTrace();
}
Select.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
JComboBox comboBox=(JComboBox) event.getSource();
Object selected = Select.getSelectedItem();
displayDate(selected);
}
});
String getMovie = (String)Select.getSelectedItem(); // New code added, directly display the Date JComboBox items
System.out.println(getMovie);
displayDate(getMovie);
Date = new JComboBox();
Date.setLocation(115,140);
Date.setSize(175, 20);
}
private void displayDate(Object selected) {
// TODO Auto-generated method stub
try {
Date.removeAllItems();
DatabaseConnection db=new DatabaseConnection();
Connection connect=db.getConnection();
String sql="Select date FROM movie WHERE title = ?";
PreparedStatement ps=connect.prepareStatement(sql);
ps.setObject(1, selected);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
String date1 = rs.getString("date");
DefaultComboBoxModel model = (DefaultComboBoxModel)Date.getModel();
if (model.getIndexOf(date1) == -1)
{
Date.addItem(date1);
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
Latest Output
Angry Bird
java.lang.NullPointerException
at gui.BuyTicket.displayDate(BuyTicket.java:131)
at gui.BuyTicket.createContentPane(BuyTicket.java:87)
at gui.BuyTicket.createAndShowGUI(BuyTicket.java:115)
at gui.HomePage$2.mouseClicked(HomePage.java:151)
at java.awt.Component.processMouseEvent(Unknown Source)
在初始化Listener后直接设置列表的第一项以触发一次监听器。
没有看具体的API如何操作，但大体是这个意思。