如何使JComboBox創建一個或多個新的JComboBox

Question

如何從JComboBox中選擇是否將選擇移除或添加到另一個JComboBox？

更具體地說，我有一個JComboBox作爲選擇的一年中的月份。我還有一個月的日子。雖然31日應該是12月份的選擇，但它不應該在2月份。任何幫助，將不勝感激。

final JComboBox<String> monthBox = new JComboBox<String>(); 
    monthBox.addItem("January"); 
    monthBox.addItem("February"); 
    monthBox.addItem("March"); 
    monthBox.addItem("April"); 
    monthBox.addItem("May"); 
    monthBox.addItem("June"); 
    monthBox.addItem("July"); 
    monthBox.addItem("August"); 
    monthBox.addItem("September"); 
    monthBox.addItem("October"); 
    monthBox.addItem("November"); 
    monthBox.addItem("December"); 

    JComboBox<String> dayBox = new JComboBox<String>(); 

Answer 1

只需裝一個ActionListener到主JComboBox和actionPerformed方法中，使用JComboBox#getSelectedItem來確定應採取何種行動。

你可以設置一個選項Map，一個在主JCheckBox每個條目這將使它更容易轉出的值

import java.awt.BorderLayout; 
import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.GridBagLayout; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.util.Calendar; 
import java.util.Date; 
import javax.swing.JComboBox; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.UIManager; 
import javax.swing.UnsupportedLookAndFeelException; 

public class JoinedComboBoxes { 

    public static void main(String[] args) { 
     new JoinedComboBoxes(); 
    } 

    public JoinedComboBoxes() { 
     EventQueue.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       try { 
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); 
       } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { 
       } 

       JFrame frame = new JFrame("Testing"); 
       frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
       frame.setLayout(new BorderLayout()); 
       frame.add(new TestPane()); 
       frame.pack(); 
       frame.setLocationRelativeTo(null); 
       frame.setVisible(true); 
      } 
     }); 
    } 

    public class TestPane extends JPanel { 

     public TestPane() { 
      final JComboBox<String> monthBox = new JComboBox<String>(); 
      monthBox.addItem("January"); 
      monthBox.addItem("February"); 
      monthBox.addItem("March"); 
      monthBox.addItem("April"); 
      monthBox.addItem("May"); 
      monthBox.addItem("June"); 
      monthBox.addItem("July"); 
      monthBox.addItem("August"); 
      monthBox.addItem("September"); 
      monthBox.addItem("October"); 
      monthBox.addItem("November"); 
      monthBox.addItem("December"); 

      setLayout(new GridBagLayout()); 
      add(monthBox); 

      final JComboBox<Integer> days = new JComboBox<>(); 
      days.setEnabled(false); 
      add(days); 

      monthBox.addActionListener(new ActionListener() { 
       @Override 
       public void actionPerformed(ActionEvent e) { 
        Calendar cal = Calendar.getInstance(); 
        String month = (String) monthBox.getSelectedItem(); 
        days.setEnabled(month != null); 
        if (month != null) { 
         int calMonth = 0; 
         switch (month) { 
          case "January": 
           calMonth = Calendar.JANUARY; 
           break; 
          case "February": 
           calMonth = Calendar.FEBRUARY; 
           break; 
          case "March": 
           calMonth = Calendar.MARCH; 
           break; 
          case "April": 
           calMonth = Calendar.APRIL; 
           break; 
          case "May": 
           calMonth = Calendar.MAY; 
           break; 
          case "June": 
           calMonth = Calendar.JUNE; 
           break; 
          case "July": 
           calMonth = Calendar.JULY; 
           break; 
          case "August": 
           calMonth = Calendar.AUGUST; 
           break; 
          case "September": 
           calMonth = Calendar.SEPTEMBER; 
           break; 
          case "October": 
           calMonth = Calendar.OCTOBER; 
           break; 
          case "November": 
           calMonth = Calendar.NOVEMBER; 
           break; 
          case "December": 
           calMonth = Calendar.DECEMBER; 
           break; 
         } 
         days.removeAllItems(); 
         cal.setTime(new Date()); // For the current year... 
         cal.set(Calendar.MONTH, calMonth); 
         int min = cal.getActualMinimum(Calendar.DATE); 
         int max = cal.getActualMaximum(Calendar.DATE); 
         for (int day = min; day <= max; day++) { 
          days.addItem(day); 
         } 
        } 
       } 
      }); 
      monthBox.setSelectedItem(null); 
     } 

     @Override 
     public Dimension getPreferredSize() { 
      return new Dimension(200, 200); 
     } 

     @Override 
     protected void paintComponent(Graphics g) { 
      super.paintComponent(g); 
      Graphics2D g2d = (Graphics2D) g.create(); 
      g2d.dispose(); 
     } 
    } 
}