import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.HeadlessException;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.ArrayList;
import java.util.List;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.JScrollPane;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

/**
*
* @author
*/
public class CoffeeMachine extends JFrame {

// default dimension of the windows
private static final int WIDTH = 400;
private static final int HEIGHT = 300;

// pre defined index of panel
private static final int COFFFE_PANEL = 0;
private static final int HOT_CHOCOLATE_PANEL = 1;
private static final int HOT_WATER_PANEL = 2;
private static final int TEA_PANEL = 3;
private static final int MIX_PANEL = 4;
private static final int START_PANEL = 5;
// number of panel
private static final int PANEL_NUMS = 6;

// pre defiend index of button
private static final int COFFFE_BUTTON = 0;
private static final int HOT_CHOCOLATE_BUTTON = 1;
private static final int HOT_WATER_BUTTON = 2;
private static final int TEA_BUTTON = 3;

/// button names
private static final String[] BEVERAGE_NAMES = {
   "Coffee", "Hot Chocolate", "Hot water", "Tea"
};
private static final String[] CONDIMENT_NAMES = {
   "sea salt", "onion", "garlic", "jalapeÃ±o pepper", "lime juice"
};

// pre defiend index of radio buttons
private static final int VERONA = 0;
private static final int PPR = 1;
private static final int DPPR = 2;
private static final int MT = 3;

// name of radio button
private static final String[] COFFEE_FLAVORS = {
   "Verona", "Pike place roast", "Decap pike place roast", "Mix two"
};

// all buttons and jlists
private JRadioButton[] flavorJRadioButtons;
private JRadioButton[] flavorJRadioButtons_mix;
private JList<String> condimentList_coffee;
private JList<String> condimentList_tea;
private JList<String> condimentList_mix;

private JButton[] beverageButtons;
private JButton[] backButtons;
private JButton[] okButtons;
private JPanel[] panels;
private JPanel currentPanel;

// listener
ButtonClickListener bcl;
ItemClickListener icl;
SelectionListioner sl;

// button group
ButtonGroup group_coffee;
ButtonGroup group_mix;

// data
private Beverage beverage;
private ArrayList<String> condiment;

public CoffeeMachine() throws HeadlessException {
   super("Cooffee Machine");
   setLayout(new BorderLayout());

   // set up 3 listerners
   bcl = new ButtonClickListener();
   icl = new ItemClickListener();
   sl = new SelectionListioner();

   // we need 2 buttons for each panel
   backButtons = new JButton[PANEL_NUMS - 1];
   okButtons = new JButton[PANEL_NUMS - 1];
   for (int i = 0; i < PANEL_NUMS - 1; i++) {
         backButtons[i] = new JButton("Back");
         okButtons[i] = new JButton("OK");
         backButtons[i].addActionListener(bcl);
         okButtons[i].addActionListener(bcl);
   }

   // we have 4 panel
   panels = new JPanel[PANEL_NUMS];
   for (int i = 0; i < panels.length; i++) {
         panels[i] = new JPanel();
         panels[i].setLayout(new BorderLayout());
   }

   // we have to use list of condiment in tea panel and codffee panel
   condimentList_coffee = new JList<>(CONDIMENT_NAMES);
   condimentList_coffee.addListSelectionListener(sl);

   condimentList_tea = new JList<>(CONDIMENT_NAMES);
   condimentList_tea.addListSelectionListener(sl);

   condimentList_mix = new JList<>(CONDIMENT_NAMES);
   condimentList_mix.addListSelectionListener(sl);

   group_coffee = new ButtonGroup();
   group_mix = new ButtonGroup();

   /// set up 5 panels
   setUpStartPanel();
   setUpCoffeePanel();
   setUpHotChocolatePanel();
   setUpHotWaterPanel();
   setUpTeaPanel();
   setUpMixPanel();

   // set up data
   beverage = null;
   condiment = new ArrayList<>();

   /// the user start at START_PANEL
   currentPanel = panels[START_PANEL];
   add(panels[START_PANEL], BorderLayout.CENTER);
   //setSize(WIDTH, HEIGHT);
   pack();
   setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   setVisible(true);
}

/**
* this panel has 2 buttons and a jlist
*/
private void setUpTeaPanel() {
   JPanel p = panels[TEA_PANEL];
   p.add(new JLabel("Tea"), BorderLayout.NORTH);
   JPanel pane = new JPanel(new BorderLayout());

   JScrollPane scrollPane1 = new JScrollPane(condimentList_tea);
   scrollPane1.setVerticalScrollBarPolicy(
            JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
   pane.add(new JLabel("Condiment"), BorderLayout.NORTH);
   pane.add(scrollPane1, BorderLayout.CENTER);
   p.add(pane, BorderLayout.CENTER);
   JPanel bottom = new JPanel(new FlowLayout());
   bottom.add(backButtons[TEA_PANEL]);
   bottom.add(okButtons[TEA_PANEL]);
   p.add(bottom, BorderLayout.SOUTH);
}

Purpose and Goal: We have discussed binary trees (BTs) in detail an...