menu.java

/* menu.java
 * learning the java OO way
 * scott nicholas <m@san.aq> jan 29 2024
 */

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

class Menu
{
    /* from <https://yohanan.org/steve/projects/java-code-conventions>
     * static variables: public, protected, package level, private
     * instance variables: ditto
     * constructors
     * methods: should be grouped by functionality
     * nested classes and interfaces
     */

    /* instance variables */
    private List<Item> items = new ArrayList<>();
    private String     name = "Menu";
    private int        maxNameLength = 0;
    private int        maxPriceLength = 0;

    /* constructors */
    public Menu(String name, Item ... items)
    {
        this.name = name;
        for (Item m : items)
        {
            this.items.add(m);
            if (m.name().length() > maxNameLength)
            {
                maxNameLength = m.name().length();
            }
            if (m.getPrice().length() > maxPriceLength)
            {
                maxPriceLength = m.getPrice().length();
            }
        }
    }

    /* methods */
    public String getName()
    {
        return this.name;
    }

    public List<Item> getItems()
    {
        return this.items;
    }

    public Item findItem(char opt)
    {
        for (Item m : this.getItems())
        {
            if (m.opt() == opt)
            {
                return m;
            }
        }
        return null;
    }

    public void displayMenu()
    {
        System.out.println(this.getName());
        for (Item m : this.getItems())
        {
            System.out.printf("%s) %-" + this.maxNameLength + "s %"
                    + this.maxPriceLength + "s\n",
                    m.opt(), m.name(), m.getPrice());
        }
        System.out.printf("Q) Quit\n");
    }

    public Item displayAndSelect(Scanner console, String prompt)
    {
        char input;
        Item item;

        while (true)
        {
            this.displayMenu();
            System.out.printf(prompt);
            try
            {
                input = console.nextLine().toUpperCase().charAt(0);
            }
            catch (Exception e)
            {
                continue; // probably hit enter without any character
            }
            // hmm
            if (input == 'Q')
            {
                return null;
            }

            item = this.findItem(input);
            if (item == null)
            {
                System.out.println("Invalid selection.");
            }
            else
            {
                return item;
            }
        }
    }

    /* nested classes */
    record Item(char opt, String name, double price)
    {
        public String getPrice()
        {
            return String.format("$%.2f", this.price());
        }
    }
} // Menu

public class menu
{
    static final Menu mainMenu = new Menu(
            "Main Menu",
            new Menu.Item('A', "item no. one", 5.25),
            new Menu.Item('B', "item2", 16.99));

    public static void main(String[] args)
    {
        Scanner console = new Scanner(System.in);
        double  total = 0.0;

        while (true)
        {
            // find what was selected
            Menu.Item selection = mainMenu.displayAndSelect(console,
                    "Selection: ");
            if (selection == null) {
                break; // XXX null means quit
            }

            System.out.printf("You selected: %s for $%.2f/ea\n",
                    selection.name(), selection.price());
            total += selection.price();
        }
        System.out.printf("Total: %.2f\n", total);
        console.close();
    }
}