为什么我的某些组件（例如Jlabel和Jcombobox）有时在使用Jbutton后不会出现？

Question

我正在尝试通过将JPanel（菜单）添加到框架并隐藏当前可见的面板（背景），从主屏幕过渡到选项菜单。我正在使用动作听众激活过渡。 有时在运行代码时（大多数时间更像），菜单的某些部分不会出现，例如Jcombobox和两个Jlabels。我没有JSlider的问题不过，但是我无法确定其他组件的问题。我尝试在我的代码末尾实现菜单和菜单>菜单>菜单。我还尝试执行frame.revalidate（）和frame.setvisible（true）。解决此问题的另一个尝试是绕菜单移动。

我使用的代码作为提供的

窗口。Java

JFrame frame;
JPanel background;
JPanel menu;
JSlider difficulty;
JLabel difficultyLabel;
JComboBox exerciseChoice;
JPanel dropDownPanel;
JLabel exerciseChoiceLabel;
JPanel difficultyPanel;

public ActionListener startButtonPressed() throws IOException {
      ActionListener temp = 
         new ActionListener() {
         
            @Override
            public void actionPerformed(ActionEvent e) {
               try {
                  background.setVisible(false);
                  menu = new JPanel();
                  menu.setLayout(new BoxLayout (menu, BoxLayout.Y_AXIS));   
                  menu.setBounds(menu.getLocation().x+50, 50, 700, 100);
                  menu.setBackground(Color.WHITE);
                  startButton.setEnabled(false);
                  createDifficultySlider(); 
                  createWorkoutDropDown();
                  
                  frame.add(menu);
                  frame.setVisible(true);
               
               } catch (IOException r) {}
            }
         
         };
      return temp;
   
   }
   
   public void createWorkoutDropDown() throws IOException {
      dropDownPanel = new JPanel();
      dropDownPanel.setLayout(new FlowLayout(FlowLayout.LEADING));
      dropDownPanel.setBackground(Color.WHITE);
      String[] choices = {"Abs", "Cardio", "Full Body", "Upper Body", "Stretches", "Lower Body"};
      exerciseChoice = new JComboBox(choices);
      exerciseChoice.setFont(new Font("Verdana", Font.PLAIN, 20));
      exerciseChoiceLabel = new JLabel("Workout Options");
      exerciseChoiceLabel.setFont(new Font("Verdana", Font.PLAIN, 20));
      dropDownPanel.add(exerciseChoiceLabel);
      dropDownPanel.add(exerciseChoice);
      menu.add(dropDownPanel);
      
      
   }
   
   public void createDifficultySlider() throws IOException {
      difficultyPanel = new JPanel();
      difficultyPanel.setLayout(new FlowLayout(FlowLayout.LEADING));
      difficultyPanel.setBackground(Color.WHITE);
      difficulty = new JSlider(JSlider.HORIZONTAL, 1, 10, 5);
      difficulty.setPreferredSize(new Dimension(difficulty.getPreferredSize().width + 60, difficulty.getPreferredSize().height + 5));
      difficultyLabel = new JLabel("Difficulty Level (Easy 1- Hard 10)");  
      difficultyLabel.setFont(new Font("Verdana", Font.PLAIN, 20));
      difficulty.setFont(new Font("Verdana", Font.PLAIN, 10)); 
      difficulty.setMajorTickSpacing(1);
      difficulty.setPaintLabels(true);
      difficulty.setPaintTicks(true);
      difficulty.setSnapToTicks(true);
      difficultyPanel.add(difficultyLabel, BorderLayout.PAGE_START);
      difficultyPanel.add(difficulty, BorderLayout.LINE_START);
      menu.add(difficultyPanel); 
   
   }

编辑：我不得不扔IOExceptions，因为我正在从驱动器中导入字体。