Object Oriented Console menu in Java

I am a Spanish programming teacher in a vocational training course and I want my students to make a CRUD exercise on arrays. I want them to start using OOP as well and as an example, I'm going to give them this example of OO Console Menu. We haven't seen Java 8 so far. Any comments or improvements would be very appreciate.

MenuOption.java

package es.primerok.menu;

/**
* Created by Miguel-David Orrico on 18/02/2017.
*/
public abstract class MenuOption {
private String option;
private String menuLine;

public MenuOption(String option, String menuLine) {
    this.option = option;
    this.menuLine = menuLine;
}

@Override
public String toString() {
    return this.option+" - "+this.menuLine;
}

public String getOption() {
    return option;
}

public abstract void doAction();

}

Menu.java

package es.primerok.menu;

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

/**
 * Created by Miguel-David Orrico on 18/02/2017.
 */
public class Menu {
private static final String OPTION_EXIT="0";
private static final String LEVEL_INDENTATION ="    ";
private List<MenuOption> menuOptions=new ArrayList<>();
private int level=0;

public Menu(){}

public Menu(int level){
    this.level=level;
}

public void add(MenuOption m){
    this.menuOptions.add(m);
}

public void loopUntilExit(){

    String input;
    try(Scanner sc=new Scanner(System.in)) {
        while (true) {
            System.out.println(this);
            input = sc.nextLine();
            if (input.equals(OPTION_EXIT)) {
                return;
            }
            boolean foundOption = false;
            for (MenuOption m : menuOptions) {
                if (m.getOption().equalsIgnoreCase(input)) {
                    m.doAction();
                    foundOption = true;
                }
            }
            if (!foundOption) {
                System.out.println("Sorry, unrecognized option");
            }
        }
    }
}

@Override
public String toString(){
    StringBuilder sb = new StringBuilder();
    sb.append("Choose an option, "+OPTION_EXIT+" to exit.\n");
    for(MenuOption m:menuOptions){
        for(int i=0;i<level;i++){
            sb.append(LEVEL_INDENTATION);
        }
        sb.append(m).append("\n");
    }
    return sb.toString();
}
}

MenuTest.java

package es.primerok.menu;

/**
 * Created by Miguel-David Orrico on 18/02/2017.
 */
public class MenuTest {
public static void main(String[] args){

    System.out.println("es.primerok.menu.Menu Test");
    Menu mainMenu=new Menu();
    Menu subMenu=new Menu(1);

    subMenu.add(new MenuOption("+","Add numbers") {
        @Override
        public void doAction() {
            System.out.println("5+7=12");
        }
    });

    subMenu.add(new MenuOption("-","Subtract some numbers") {
        @Override
        public void doAction() {

            System.out.println("we're subtracting 6 and 5. The result is 1");
        }
    });
    mainMenu.add(new MenuOption("1","Option number 1") {
        @Override
        public void doAction() {
            System.out.println("This is number one");
        }
    });
    mainMenu.add(new MenuOption("A","Print an A") {
        @Override
        public void doAction() {
            System.out.println("I'm in Option A");
        }
    });
    mainMenu.add(new MenuOption("sub","This has a submenu") {
        @Override
        public void doAction() {
            subMenu.loopUntilExit();
        }
    });

    mainMenu.loopUntilExit();
}
}