import javax.swing.*;

public class Exam2 {

  private static JPanel createPanel() {
    JPanel panel=new JPanel();
    for(int i=0;i<3;i++)
      panel.add(new JButton("button "+i));
    return panel;
  }

  public static void main(String[] args) {
    JFrame frame=new JFrame();
    
    frame.setContentPane(createPanel());
    
    frame.setSize(400,300);
    frame.show();
  }
}