Saving objects from different classes into the same array

Processing Coding Questions
9

I have my arrays set like this in my main area:

Wall[] walls = new Wall[100];
Gate[] gates = new Gate[100];
Player1[] player = new Player1[100];
Goal[] goals = new Goal[100];
Key[] keys = new Key[100];
Enemy[] enemies = new Enemy[100];
Level[] levels = new Level[100];

The levels array creates an error.
Once I have my arbitrary blank array of levels i can then say levels[0].append(walls[0]);
Or loop through a specific number of walls like

for (int i = 0; i <= 4; i ++){
levels[0].append(walls[i]);
}

and do that for every set of walls, players, gates, and everything for levels[0], then levels[1], until I’m done with everything, then I have all my levels set in a neat array.

I completely forgot about the implements ArrayList thing… I can just append every element corresponding to particular levels into objects levels[i]…

My level class has a mistake or two cuz there’s different arraylists at beginning which I don’t need.

class Level{
  ArrayList<Wall> walls;
  ArrayList<Key> keys;
  ArrayList<Goal> goals;
  
  ArrayList<GameElement> elements = new ArrayList<GameElement>();
  
  

  Level() {
    walls = new ArrayList<Wall>();
    //gates = new ArrayList<Gate>();
    keys = new ArrayList<Key>();
    goals = new ArrayList<Goal>();
  }

  void draw() { 
    for (int i = 0; i < walls.size(); i++) { // normal for loop
      walls.get(i).draw(); // use .get() on ArrayLists
    }
    for (Key k : keys) { // for each loop, effectively the same as above but a little quicker to write once you understand how it works
      k.draw(); // k is equal to the current key so no need for .get()
    }
    // loop through doors also
  }

}

// In your main program store all the levels in another ArrayList and just key a variable to say what level you're on
ArrayList<Level> levels = new ArrayList<Level>();
int currentLevel = 1;

// You can start creating level in setup by doing something like this


// so on and so forth
// then add level to levels ArrayList and repeat

I think the constructor confuses me, shouldn’t there be an object of some kind in the constructor so when I implement the specific level objects and append an element, the level class knows where to put the element?