Swing Jcombobox將第一個元素設置爲默認選中的

Question

String[] bookArray={"a","b","c"}; 
    JComboBox bookComboBox = new JComboBox(bookArray); 
    bookComboBox.setSelectedIndex(0); 
    bookComboBox.addActionListener(new ActionListener() { 
     public void actionPerformed(ActionEvent e) { 
      JComboBox cb= (JComboBox) e.getSource(); 
      bookNameSelected=(String) cb.getSelectedItem(); 
      System.out.println("book name selected:"+bookNameSelected); 
      } 
    }); 

下拉的第一個元素顯示爲默認值，但如果用戶未選擇任何值，則不會將其作爲默認選定值傳遞。

Answer 1

移動bookComboBox.setSelectedIndex(0);的ActionListener登記後，這允許ActionListener被觸發，並設置bookNameSelected

String[] bookArray = {"a", "b", "c"}; 
JComboBox bookComboBox = new JComboBox(bookArray); 
bookComboBox.addActionListener(new ActionListener() { 
    public void actionPerformed(ActionEvent e) { 
     JComboBox cb = (JComboBox) e.getSource(); 
     bookNameSelected = (String) cb.getSelectedItem(); 
     System.out.println("book name selected:" + bookNameSelected); 
    } 
}); 
bookComboBox.setSelectedIndex(0);