Parameters of method not working but work when directly coded

Newbie & Debugging Questions
#1

Hey guys I have a rather odd (or it may just be my stupidity) question. I have a little animation method which is shown below:

void setSprites(TextureRegion mainMob, TextureRegion upMob_STILL,
			TextureRegion upMob_LEFT, TextureRegion upMob_RIGHT,
			TextureRegion downMob_STILL, TextureRegion downMob_LEFT,
			TextureRegion downMob_RIGHT, TextureRegion rightMob_STILL,
			TextureRegion rightMob_LEFT, TextureRegion rightMob_RIGHT,
			TextureRegion leftMob_STILL, TextureRegion leftMob_LEFT,
			TextureRegion leftMob_RIGHT) {
		if (timer < 4)
			timer += .1f;
		else
			timer = 0;

		// walking right animation
		if (direction == 3) {
			if (timer < 1) {
				mainMob = rightMob_STILL;
			} else if (timer > 1 && timer < 2) {
				mainMob = rightMob_LEFT;
			} else if (timer > 2 && timer < 3) {
				mainMob = rightMob_STILL;
			} else if (timer > 3) {
				mainMob = rightMob_RIGHT;
			}
		}

		// walking left animation
		if (direction == 2) {
			if (timer < 1) {
				mainMob = leftMob_STILL;
			} else if (timer > 1 && timer < 2) {
				mainMob = leftMob_LEFT;
			} else if (timer > 2 && timer < 3) {
				mainMob = leftMob_STILL;
			} else if (timer > 3) {
				mainMob = leftMob_RIGHT;
			}
		}

		// walking up animation
		if (direction == 0) {
			if (timer < 1) {
				mainMob = upMob_STILL;
			} else if (timer > 1 && timer < 2) {
				mainMob = upMob_LEFT;
			} else if (timer > 2 && timer < 3) {
				mainMob = upMob_STILL;
			} else if (timer > 3) {
				mainMob = upMob_RIGHT;
			}
		}

		// walking down animation
		if (direction == 1) {
			if (timer < 1) {
				mainMob = downMob_STILL;
			} else if (timer > 1 && timer < 2) {
				mainMob = downMob_LEFT;
			} else if (timer > 2 && timer < 3) {
				mainMob = downMob_STILL;
			} else if (timer > 3) {
				mainMob = downMob_RIGHT;
			}
		}
	}

As you can see I have quite a lot of parameters, but that should all be working. I call the method appropriately, but the “mainMob” texture region is never changed. If I avoid using these parameters by doing this

	void setSprites() {
		if (timer < 4)
			timer += .1f;
		else
			timer = 0;

		// walking Assets.right animation
		if (direction == 3) {
			if (timer < 1) {
				Assets.mainCreeper = Assets.rightCreeper_STILL;
			} else if (timer > 1 && timer < 2) {
				Assets.mainCreeper = Assets.rightCreeper_LEFT;
			} else if (timer > 2 && timer < 3) {
				Assets.mainCreeper = Assets.rightCreeper_STILL;
			} else if (timer > 3) {
				Assets.mainCreeper = Assets.rightCreeper_RIGHT;
			}
		}

		// walking left animation
		if (direction == 2) {
			if (timer < 1) {
				Assets.mainCreeper = Assets.leftCreeper_STILL;
			} else if (timer > 1 && timer < 2) {
				Assets.mainCreeper = Assets.leftCreeper_LEFT;
			} else if (timer > 2 && timer < 3) {
				Assets.mainCreeper = Assets.leftCreeper_STILL;
			} else if (timer > 3) {
				Assets.mainCreeper = Assets.leftCreeper_RIGHT;
			}
		}

		// walking Assets.up animation
		if (direction == 0) {
			if (timer < 1) {
				Assets.mainCreeper = Assets.upCreeper_STILL;
			} else if (timer > 1 && timer < 2) {
				Assets.mainCreeper = Assets.upCreeper_LEFT;
			} else if (timer > 2 && timer < 3) {
				Assets.mainCreeper = Assets.upCreeper_STILL;
			} else if (timer > 3) {
				Assets.mainCreeper = Assets.upCreeper_RIGHT;
			}
		}

		// walking Assets.down animation
		if (direction == 1) {
			if (timer < 1) {
				Assets.mainCreeper = Assets.downCreeper_STILL;
			} else if (timer > 1 && timer < 2) {
				Assets.mainCreeper = Assets.downCreeper_LEFT;
			} else if (timer > 2 && timer < 3) {
				Assets.mainCreeper = Assets.downCreeper_STILL;
			} else if (timer > 3) {
				Assets.mainCreeper = Assets.downCreeper_RIGHT;
			}
		}
	}

Everything works great this way. The “Assets.mainCreeper” is changed to whatever the current animation state should be. The only reason I can’t do it like that is that I have many different types of mobs so I would want to use parameters rather than making a class or method specific for each mob type. Is there some specific reason that using parameters makes this not work at all? From my code (in the parameter example) everything is the same as the parameterless example which would make me think it would work. Is there something with using parameters that stops this from working properly? I know this may be a long question but I appreciate the help!

P.s. after the current image is set to the “mainMob” texture region or the “Assets.mainCreeper” i draw that texture region seems obvious but i thought i would include it.

#2

Ok , It seems you are confusing lots of stuff.
JAVA is pass by value, and when you pass an object, you pass it’s value (Which is it’s “pointer” ) lets say that.
When you pass anything to a function, it just copies its value to a variable on the stack for that function.
When you change the value, you are changing it inside the stack on that function.
This is an usual beginner mistake.

try this.
int i = 6;
public void change(int i) { i =56; } change(i) print(i) and see what happens.
what happens is you set aside a variable for that function. get it?

it is as if you were doing.
Sprite s1; setSprite(Sprite s) will do s = s1; then s = newSprite; it doesn’t affect your s1 that you passed.
How you fix it? you change the state of the sprite ( sprite.setStuff) , or you encapsulate the sprite in some object and change the state of that object, or you return a list or something of new textures/stuff

#3

I was wondering if it was that, and it turns out it is. Would a getter / setter solve this problem? Since calling a setter would change the original value rather than the copy, if my logic is right here…

#4

In basic terms:

You have a lot of objects stored in RAM.
There are ‘pointers’ which store the position of the object in RAM.

When you call a function, you pass a copy of the pointer to the function, which then finds the object which it points at.
Any changes to the object affect the object, which will change what’s being referenced by all pointers, but:
If you reassign the variable, it changes the local value of the pointer, not the value of the object, and not the value of the pointer in other locations.

Here is a workaround to help explain my point:


class Pointer <T extends Object>
{
	public T value;

	public Pointer(T value)
	{
		this.value = value;
	}
}

(Generics aren’t neccessary, you can change it to just a certain class if you want)

Then you can change the value and it will change in all locations of the class.

DISCLAIMER: I do not recommend using that workaround. It was just to help explain the problem. Please just redesign your code.

#5

I think I understand what I am doing wrong here but what is a good way to redesign my code?

#6

Remove mainMob from the method parameters as it is useless, change [icode]setSprites()[/icode] to return mainMob, and when calling the function, do this:


mainMob = setSprite(/*...all the sprites here etc.*/)

Also, this code has too much of a brute-force approach just for simple animations. I recommend redesigning for future projects.

#7

Everything is looking good now! Thank you. I too thought this looked a little excessive but I had no other ideas on how to make it simpler :frowning: