Java ActionListener set JFrame background via action command

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class Main extends JFrame implements ActionListener {
   private final String ACTION_ON = "LIGHT ON";
   private final String ACTION_OFF = "LIGHT OFF";
   private final String ACTION_CYCLE = "CYCLE COLOR";
   //from w ww . j  a va 2s  .  c om
   private final Color[] COLORS = new Color[]{
         Color.white,
         Color.green,
         Color.red,
         Color.yellow,
         Color.orange,
         Color.pink
   };
   
   private int currentColor = 0;
   private boolean isLightOn = false;
   
   public Main() {
      setTitle("Disco Light Party Frame");
      setLayout(new FlowLayout());
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      
      JButton btnOffOn = new JButton("Lights On");
      JButton btnColor = new JButton("Cycle Color");
      
      btnOffOn.setActionCommand(ACTION_ON);
      btnColor.setActionCommand(ACTION_CYCLE);
      
      btnOffOn.addActionListener(this);
      btnColor.addActionListener(this);
      getContentPane().add(btnOffOn);
      getContentPane().add(btnColor);
      pack();
      setVisible(true);
   }
   
   @Override
   public void actionPerformed(ActionEvent ev) {
      String action = ev.getActionCommand();
      System.err.println("Got action "+action);
      switch (action) {
      case ACTION_ON:
         isLightOn = true;
         getContentPane().setBackground(COLORS[currentColor]);
         ((JButton) ev.getSource()).setText("Lights Off");
         ((JButton) ev.getSource()).setActionCommand(ACTION_OFF);
         break;
      case ACTION_OFF:
         isLightOn = false;
         getContentPane().setBackground(Color.black);
         ((JButton) ev.getSource()).setText("Lights On");
         ((JButton) ev.getSource()).setActionCommand(ACTION_ON);
         break;
      case ACTION_CYCLE:
         if (isLightOn)
            getContentPane().setBackground(COLORS[++currentColor
               % COLORS.length]);
         break;
      }
   }
   
   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            new Main();
      }
      });
   }
}