爲什麼我的代碼不能同時運行兩個面板？它沒有顯示任何東西，當我運行它，但它編譯

Question

想知道爲什麼這段代碼不會運行。它編譯，但沒有顯示GUI或任何由於某種原因，請幫助！這是一個2幀，最終3幀的程序。如果我刪除了迄今爲止所做的一切，但只保留一個組合框/一個面板的作用，並顯示/編譯完美。

反正這裏是代碼！

import java.awt.BorderLayout; 
    import java.awt.event.ActionEvent; 
    import java.awt.event.ActionListener; 

    import javax.swing.*; 

    public class FastFood implements ActionListener 
    { 
    JFrame frame; 
    JPanel contentpane1; //this panel will include cheese burger, chicken sandwich, hot dog, pizza, and salad 
    JPanel contentpane2; // this pane will include side salad, french fried, or apple slice 
    JPanel contentpane3; // this panel will include coke, diet coke, sprite, ice tea, coffee, root beer, or water 

    JComboBox maindish; //combo box for maindishes 
    JComboBox sides; //box for sides 
    JComboBox drink; //box for drinks 

    JLabel fastfoodp1; // label for main dish 
    JLabel fastfoodp2; //label for sides 
    JLabel fastfoodp3; // label for drinks 
    JLabel c1; // cost for main dish 
    JLabel c2; //cost for drink 
    JLabel c3; //cost for sides 
    JLabel cost; //label to display the total cost 

    public FastFood() 
    {  
     frame = new JFrame("Order your fastfood!"); //sets up frame title 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
     //all of this code is for the maindish 
     contentpane1 = new JPanel(); //creats panel object 
     contentpane1.setLayout(new BoxLayout(contentpane1, BoxLayout.PAGE_AXIS)); //creates layout 
     contentpane1.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5)); //creates border 
     //next three lines of code set up the label to prompt user for main dish 
     fastfoodp1 = new JLabel("Select a main dish"); 
     fastfoodp1.setAlignmentX(JLabel.LEFT_ALIGNMENT); 
     contentpane1.add(fastfoodp1); 

     //next code sets up the combo box options and adds it to the panel 
     String[] MainDishes = {"Cheese Burger", "Chicken Sandwich", "Hot Dog", "Pizza", "Salad" }; 
     maindish = new JComboBox(MainDishes); 
     maindish.setAlignmentX(JComboBox.LEFT_ALIGNMENT); 
     maindish.setSelectedIndex(0); 
     maindish.addActionListener(this); 
     contentpane1.add(maindish); 

     //sets up price label for selected item 
     c1 = new JLabel("Cost of Main Dish"); 
     c1.setBorder(BorderFactory.createEmptyBorder(20, 0, 0, 0)); 
     contentpane1.add(c1); 

     //next code is for sides 

     contentpane2 = new JPanel(); 
     contentpane2.setLayout(new BoxLayout(contentpane1, BoxLayout.PAGE_AXIS)); 
     contentpane2.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5)); 

     //next codes set up label to prompt user for sides 
     fastfoodp2 = new JLabel("Select a side"); 
     fastfoodp2.setAlignmentX(JLabel.CENTER_ALIGNMENT); 
     contentpane2.add(fastfoodp2); 

     //next code sets up the combo box options and adds it to the panel 
     String[] SideDishes = {"Side Salad", "Frend Fries", "Apple Slice" }; 
     sides = new JComboBox(SideDishes); 
     sides.setAlignmentX(JComboBox.CENTER_ALIGNMENT); 
     sides.setSelectedIndex(0); 
     sides.addActionListener(this); 
     contentpane2.add(sides); 

     //sets up price label for selected item 

     c2 = new JLabel("Cost of Side Dish"); 
     c2.setBorder(BorderFactory.createEmptyBorder(20,0,0,0)); 
     contentpane2.add(c2); 

     //next code is for Drinks 

     //makes it visible 
     frame.setContentPane(contentpane1); 
     frame.pack(); 
     frame.setVisible(true); 

     frame.setContentPane(contentpane2); 
     frame.pack(); 
     frame.setVisible(true); 

     frame.add(contentpane1, BorderLayout.WEST); 
     frame.add(contentpane2, BorderLayout.CENTER); 

     //next code is for sides  
    } 

    public void actionPerformed(ActionEvent event) 
    { 
     JComboBox comboBox = (JComboBox)event.getSource(); 
     String maindishname =(String)comboBox.getSelectedItem(); 
     if (maindishname == "Cheeese Burger") 
     { 
      c1.setText("$3.50 for Cheese Burger"); 
     } 
     else if (maindishname == "Chicken Sandwich") 
     { 
      c1.setText("$2.50 for Chicken Sandwich"); 
     } 
     else if (maindishname == "Hot Dog") 
     { 
      c1.setText("$2.50 for Hot Dog"); 
     } 
     else if (maindishname == "Pizza") 
     { 
      c1.setText("$2.00 for Pizza"); 
     } 
     else if (maindishname == "Salad") 
     { 
      c1.setText("$1.50 for Salad"); 
     } 

     JComboBox sides = (JComboBox)event.getSource(); 
     String sidedishname = (String)sides.getSelectedItem(); 

     if(sidedishname == "Side Salad") 
     { 
      c2.setText("$0.50 for Side Salad"); 
     } 
     else if (sidedishname == "French Fries") 
     { 
      c2.setText("$1.00 for French Fries"); 
     } 
     else if (sidedishname == "Apple Slice") 
     { 
      c2.setText("$0.75 for Applie Slice"); 
     } 
    } 

     private static void runGUI() 
     { 
      JFrame.setDefaultLookAndFeelDecorated(true); 
      FastFood food = new FastFood(); 
     } 
     public static void main(String[] args) 
     {    
      javax.swing.SwingUtilities.invokeLater(new Runnable() {public void run() {runGUI();} }); 
     } 
} 

Answer 1

BoxLayout不允許目標組件的共享。更換

contentpane2.setLayout(new BoxLayout(contentpane1, BoxLayout.PAGE_AXIS)); 

與

contentpane2.setLayout(new BoxLayout(contentpane2, BoxLayout.PAGE_AXIS)); 

注意使用contentpane2爲目標Component。

如果要將組件添加到JFrame的BorderLayout的各個位置，請勿使用JFrame#setContentPane。

你需要重寫getPreferredSize在JPanelscontentpane1和contentpane2使用pack促進正確的尺寸。

同時請確保調用JFrame#setVisible將所有組件的JFrame後。