Java BoxLayout .invalidateLayout (Container target)

public void invalidateLayout(Container target)

import java.awt.BorderLayout;
//  ww w .  j  a v a 2  s.co m
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main {

  public static void main(String[] a) {
    JFrame frame = new JFrame("Alignment Example");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    String labels[] = { "--", "----", "--------", "------------" };

    JPanel container = new JPanel();
    BoxLayout layout = new BoxLayout(container, BoxLayout.Y_AXIS);
    layout.invalidateLayout(container);
    container.setLayout(layout);

    for (int i = 0; i < labels.length; i++) {
      JButton button = new JButton(labels[i]);
      container.add(button);
    }

    frame.add(container, BorderLayout.CENTER);

    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}