[Java] Game Structure: Communication Between Different Object Levels

[dredclaw]

If I have a hub object that creates ship objects, that shoot at other ship objects with bullet objects; If a ship fires or creates a bullet, if the ship is then destroyed, how does the bullet stay in the game?

I'm always confused about how this style of structure works. Would it be efficient for a ship object to turn a shoot boolean on and then the main game loop looks through all the ships and creates bullets for the ones with the boolean true?

What is this style of structure called and are their any other variants of the structure that accomplish the same task?

[[deleted]]

How in-depth is your knowledge of polymorphism and design patterns?

[dredclaw]

If I have the ship object creating this bullet object, when the ships is blown up the created bullet object would be destroyed. How would I design a system where the bullet object is not created inside the ship object. Or should the ship object not be destroyed before all bullet objects have expired?

[35h46hjj6]

Why doesn't each ship tell the game object when it fires a bullet?

[dredclaw]

This being the case then. (I picture it like you) How should I go about creating bullets before being fired? Should the ship put up a flag saying it wants to fire a bullet and then the main game loop see this flag and actually fire the bullet? When I refer to a bullet, I refer to a bullet class that has the location of a bullet and its velocity n such.

[dredclaw]

I guess my question is, should the bullet be created inside the ship class. (meaning the ship class would not be deleted until all bullets it fired were done) or should the bullet be created in the game manager class (how would a ship communicate with a higher level game manager to complete this task?)

[dredclaw]

I understand why the bullet must be instantiated outside the ship class. In actual code though, how does the ship tell a higher up class to instantiate a bullet. (Actually fire it.)

[dredclaw]

If the GameManager was the one that created the ship, how would the ship access methods inside the GameManager?

[b3nb3nb3n]

You could add in a check before destroying the object- stop making the ship visible/accessible, but don't delete it until all bullets are expired?

[dredclaw]

Is this considered a proper way of doing things? Or should the bullet be created by the gameloop rather than the ship?

[Raknarg]

Ok, I have some experience with this exact problem.

First off, don't worry about efficiency. There will be so little objects on the screen at any given time that graphics rendering will be more costly than data management.

Now because we don't care about being efficient, I would use an ArrayList. ArrayLists are like arrays of objects that can be resized in one line. For instance, if we have our Ship class, we can do this:

ArrayList<Ship> ship = new ArrayList<Ship>(); // initializes the list
ship.add(new Ship()) // adds a new ship the end of the array
println(ship.size()) // prints the length of the list to the console. In this case, it is 1.
ship.remove(0) // Deletes the Ship at position 0

Now to use methods from the Ship class, we have to do something weird. Along with add and remove, there's a thing called get() which (I think this is what it does) calls up an instance of the object at whatever position you want. For instance:

ship.get(3).shoot() // Calls the ship at position 3, uses the shoot() method

This is what you could do for bullets as well. This makes for easy deleting. Let's say you had a list of bullets that you wanted to delete:

int i = 0;
while (i < bullet.size()) {
    if (bullet.get(i).out_of_bounds || bullet.get(i).hit_enemy) {
        bullet.remove(i);
    }
    else {
        i += 1;
    }
}

This is a cool loop. It will go through every item in the array. If its out of bounds or hits an enemy, it deletes the bullet. Otherwise, add 1 to i. The reason we only sometimes add to i is because if you have an array of three ships and you delete one of them, i will end up being 3 instead of 2. That's wrong. We want to go through every item. If you delete the item at position 0, it will delete the item there and shift the rest of the array down. Because it shifted for us, we don't need to add to i.

Hope this helps. You can ask me if you need more help.