BlueJ Wie programmiere ich das?

(…) I use a base library provided by the school in BlueJ.

I guess it’s the basicUTF8151026.jar.

Now I want you to select your maps you want to use in an extra menu (…)

You need a class that can describe/represent a card. For the selection menu, you can create an array that will then display all the cards that are available.

Visually, the cards could be displayed by means of buttons (Buttons) are shown. So you use a loop over the array and place a single entry Button and add it to the graphical surface. Each button will also be equipped with a Buttons in which the card associated with the button is inserted into a new array (or a list).

This is indicated as follows:

private int maximalErlaubteKartenanzahl = 10;
private Karte[] ausgewaehlteKarten = new Karte[maximalErlaubteKartenanzahl];
private int aktuellGewaehlteKartenzahl = 0;

/* ... */

for (Karte karte : auswahlKarten) {
  Knopf knopf = new Knopf(/* ... */);
  knopf.setzeKnopfLauscher(gedrueckterKnopf -> {
    if (aktuellGewaehlteKartenzahl < maximalErlaubteKartenanzahl) {
      ausgewaehlteKarten[aktuellGewaehlteKartenzahl++] = karte;
    }
  });
}

The setzebutton-Method is passed an anonymous function. This can remember the values from the current context. At the push of a button, it is executed and can insert the card object that it has noticed in its definition into the array that stores the selected cards.

(...) and then appear in the class: Arena (...).

If the player decides to start the game (e.g. by clicking on a start button), you can start a new game Arena- Create object and pass the selected cards. Either directly via the constructor or via a setter method.

Example:

class Arena {
  private Karte[] spielkarten;

  public Arena(Karte[] spielkarten) {
    this.spielkarten = spielkarten;
  }
}

// create Arena object
Karte[] karten = // get karten ...
Arena arena = new Arena(karten);