Use GroupLayout in Java

/*from  w  w w  .  ja v  a  2  s  . c o  m*/
import javax.swing.GroupLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main {
  public static void main(String[] args) {
    JFrame frame = new JFrame();
    JPanel panel = new JPanel();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    GroupLayout layout = new GroupLayout(panel);
    panel.setLayout(layout);

    JButton buttonD = new JButton("D");
    JButton buttonR = new JButton("R");
    JButton buttonY = new JButton("Y");
    JButton buttonO = new JButton("O");
    JButton buttonT = new JButton("T");

    GroupLayout.SequentialGroup leftToRight = layout.createSequentialGroup();

    leftToRight.addComponent(buttonD);
    GroupLayout.ParallelGroup columnMiddle = layout.createParallelGroup();
    columnMiddle.addComponent(buttonR);
    columnMiddle.addComponent(buttonO);
    columnMiddle.addComponent(buttonT);
    leftToRight.addGroup(columnMiddle);
    leftToRight.addComponent(buttonY);

    GroupLayout.SequentialGroup topToBottom = layout.createSequentialGroup();
    GroupLayout.ParallelGroup rowTop = layout.createParallelGroup();
    rowTop.addComponent(buttonD);
    rowTop.addComponent(buttonR);
    rowTop.addComponent(buttonY);
    topToBottom.addGroup(rowTop);
    topToBottom.addComponent(buttonO);
    topToBottom.addComponent(buttonT);

    layout.setHorizontalGroup(leftToRight);
    layout.setVerticalGroup(topToBottom);

    frame.add(panel);
    frame.pack();
    frame.setVisible(true);
  }
}