code works but why?

[game2d]

http://pastebin.com/v4Jd1yTc

hi I am following a tutorial which shows how to create tileMap game in java. But i cant seem to understand some of the methods and variables. main code i post it on pastebin.com take a look.

problem is I cant seem to understand what is method calculateCorner s is doing.

calculateCorners(x, toy);
        /*******************************/
	/*** calculateCorners method ***/
	public void calculateCorners(double x, double y) {
		int leftTile = tileMap.getColTile((int) (x - width / 2));
		int rightTile = tileMap.getColTile((int) (x + width / 2) - 1);
		int topTile = tileMap.getColTile((int) (y - height / 2));
		int bottomTile = tileMap.getColTile((int) (y + height / 2) - 1);

		// check if player can move to tiles
		// 0 = cant move up
		topLeft = tileMap.getTile(topTile, leftTile) == 0;
		topRight = tileMap.getTile(topTile, rightTile) == 0;
		bottomLeft = tileMap.getTile(bottomTile, leftTile) == 0;
		bottomRight = tileMap.getTile(bottomTile, rightTile) == 0;
	}// End of calculateCorners

first question is:
i understand that topLeft, are booleans to check if player can move there or not. But why only 4 boolean? dont you need "top, topLeft, topRight, etc" what is player just jump up? than dont you get boolean "top".

2nd question is:
can you guys explain "int leftTile, rightTile .. etc" variables?

also why we are doing (x-width/2)?

also try to explain as much as you can bc i dont understand this.

[Nepomuk]

Without knowing the context it is difficult to tell you what anything in your code is for. Is the tutorial online and if so, can you paste a link to it? You don't even say what kind of game we're talking about. Also, where is the implementation of the TileMap class? With more information, I'm sure we'll be able to help you understand the code.