I'm trying to create a console based Menu class. I want the class to contain an array (named options) of MenuOption objects which each have a label (String), text (String), and code (TBD) property. The idea is that I want users to input a string and the menu will execute the relevant code with something close to the following:

for (MenuOption option: options)
{
if (input.equals(option.label)) execute option.code;
}

I feel like theres probably a way to do this using lambda functions, but I've been hitting dead ends for the last couple of hours. Any suggestions are appreciated.

CodePudding user response：

This is the classic Java 8 version, fully implemented.

package stackoverflow;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Objects;

public class ConsoleMenu {

    static public class MenuOption {
        public final String     label;
        public final String     text;
        public final Runnable   code;
        public MenuOption(final String pLabel, final String pText, final Runnable pLambda) {
            label = pLabel;
            text = pText;
            code = pLambda;
        }
    }



    public static void main(final String[] args) throws IOException {
        final ArrayList<MenuOption> options = new ArrayList<>();
        options.add(new MenuOption("Option A", "A", () -> System.out.println("Hello this is A")));
        options.add(new MenuOption("Option B", "B", () -> {
            System.out.print("Hello this is B");
            System.out.println(" in multiple lines Lambda");
        }));


        System.out.println(" - - - Menu - - - ");
        for (final MenuOption mo : options) {
            System.out.println("\t"   mo.label   "\t"   mo.text);
        }
        System.out.println("Enter your choice:");
        try (final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));) {
            final String line = br.readLine().toLowerCase();
            for (final MenuOption mo : options) {
                if (Objects.equals(line, mo.text.toLowerCase())) {
                    System.out.println("You chose "   mo.label);
                    mo.code.run();
                    break;
                }
            }
        }

        System.out.println("All done.");
    }

}

CodePudding user response：

You’re on the right track. Try something like:

public record MenuOption(String label,
                         String text,
                         Runnable action) {
    // Deliberately empty.
}

You can, as you suspected, construct them with lambdas:

MenuOption printOption = new MenuOption(
    "Print",
    "Send formatted data to a printer",
    () -> printData());

MenuOption exitOption = new MenuOption(
    "Exit",
    "Close application",
    () -> System.exit(0));

If you’re stuck with an older version of Java, you can just make a regular class which is equivalent to a record:

public class MenuOption {
    private String label;
    private String text;
    private Runnable action;

    public MenuOption(String label,
                      String text,
                      Runnable action) {
        this.label = label;
        this.text = text;
        this.action = action;
    }

    public String getLabel() {
        return label;
    }

    public String getText() {
        return text;
    }

    public Runnable getAction() {
        return action;
    }
}