Java 布局不显示组件(有时)

I'm writing a MathQuiz for my pupils including JLatexMath for rendering and jinput for the buzzers. The problem is, that sometimes (like every fourth time) when I start the program, none of the components are visible. They appear after resizing the JFrame. First I was thinking of Bugs in the jinput or jlatexMath libraries, but I do get the same Error even with this minimal Code:

public class Shell extends JFrame{

  private JButton button1;
  private JButton button2;
  private Formula formula;

  public Shell() {
    super("blaBla");
    this.setSize(800, 600);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
    this.setLayout(new BoxLayout(this.getContentPane(), BoxLayout.Y_AXIS));
    Box b = Box.createHorizontalBox();
    button1 = new JButton(" ");
    button1.setEnabled(false);
    b.add(button1);
    b.add(Box.createHorizontalGlue());
    button2 = new JButton(" ");
    button2.setEnabled(false);
    b.add(button2);
    add(b);
    JPanel formulaPanel = new JPanel();
    add(Box.createVerticalStrut(20));
    add(formulaPanel);
  } 

  public static void main(String[] args) {
    Shell s = new Shell();
  }
}

代码有什么问题?

推荐答案

首先将 setVisible(true); 移动到构造函数的末尾.

public Shell() {
    super("blaBla");
    this.setSize(800, 600);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setVisible(true);
    //...
} 

public Shell() {
    super("blaBla");
    //...
    add(Box.createVerticalStrut(20));
    add(formulaPanel);
    setVisible(true);
}