import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JMenu;
import javax.swing.JMenuItem;
import javax.swing.JMenuBar;
import java.awt.GridLayout;
import java.awt.Color;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class MenuDemo extends JFrame implements ActionListener {

    public static final int WIDTH = 300;    // extending JFrame because MenuDemo needs a JFrame
                                          // gui needs a JFrame..the outline.
                                          // implementing ActionListener whenever we need to perform actions
                                          // implements are for interfaces and interfaces have abstract methods no complete methods
    public static final int HEIGHT = 200;
                                        private static final JButton JButton = null;

    private JPanel greenPanel; // creating JPanels
    private JPanel whitePanel;
    private JPanel grayPanel;

    public static void main(String[] args)
    {
        MenuDemo gui = new MenuDemo();
        gui.setVisible(true);

    }

    public MenuDemo() // MenuDemo constructor
    {
        super("Menu Demonstration");  //
        setSize(WIDTH, HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new GridLayout(1, 3));

        greenPanel = new JPanel();
        greenPanel.setBackground(Color.LIGHT_GRAY);
        add(greenPanel);

        whitePanel = new JPanel();
        whitePanel.setBackground(Color.LIGHT_GRAY);
        add(whitePanel);

        grayPanel = new JPanel();
        grayPanel.setBackground(Color.LIGHT_GRAY);
        add(grayPanel);

        JMenu colorMenu = new JMenu("Add Colors");

        JMenuItem greenChoice = new JMenuItem("Green");
        greenChoice.addActionListener(this);
        colorMenu.add(greenChoice);

        JMenuItem whiteChoice = new JMenuItem("White");
        whiteChoice.addActionListener(this);
        colorMenu.add(whiteChoise);

        JMenuItem grayChoice = new JMenuItem("Gray");
        grayChoice.addActionListener(this);
        colorMenu.add(grayChoice);

        JMenuBar bar = new JMenuBar();
        bar.add(colorMenu);
        setJMenuBar(bar);

    }

    public void actionPerformed(ActionEvent e)
    {
        String buttonSring = e.getActionCommand();

        if (buttonString.equals("Green"))
            greenPanel.setBckground(Color.GREEN);
        else if (buttonString.equals("White"))
            whitePanel.setBackground(Color.WHITE);
        else if (buttonString.equals("Gray"))
            grayPanel.setBackground(Color.GRAY);
        else
            System.out.println("Unexpected error.");
    }
}