Question on A star for shortest path

[toucan]

I'm trying to find the shortest path between two locations in a 2D array with only horizontal and vertical moves allowed (Manhattan distance).

I've tried to convert the pseudocode from Wikipedia's article on the A star algorithm (http://en.wikipedia.org/wiki/A_star) into Java, but it doesn't work. Note: the game works properly using a recursive path-finding algorithm that doesn't guarantee a shortest path, so the bug must be here.

Can anyone please tell me what I'm doing wrong?

/ A* algorithm wikipedia
	public ArrayList<OrderedCoordinatePair> aStar(int irow, int icol, int frow,
			int fcol) {
		// The set of nodes already evaluated.
		closedSet = new ArrayList<OrderedCoordinatePair>();

		// The set of tentative nodes to be evaluated.
		openSet = new ArrayList<OrderedCoordinatePair>();
		openSet.add(allCells[irow][icol]);

		// Distance from start along optimal path.
		gScore = new int[NUMROWS][NUMCOLS];
		gScore[irow][icol] = 0;

		// heuristic estimate of distance from start to goal
		hScore = new int[NUMROWS][NUMCOLS];
		hScore[irow][icol] = Math.abs(frow - irow) + Math.abs(fcol - icol);

		// Estimated total distance from start to goal through y.
		fScore = new int[NUMROWS][NUMCOLS];
		fScore[irow][icol] = hScore[irow][icol];

		while (!openSet.isEmpty()) {
			// x := the node in openset having the lowest f_score[] value
			currentNode = openSet.get(0);
			for (int i = 0; i < openSet.size(); i++) {
				if (fScore[openSet.get(i).getRowNum()][openSet.get(i)
						.getColNum()] < fScore[currentNode.getRowNum()][currentNode
						.getColNum()]) {
					currentNode = openSet.get(i);
				}
			}

			if (currentNode.getRowNum() == frow
					&& currentNode.getColNum() == fcol) {
				shortestPath.clear();
				resetParentNodes();
				return reconstructPath(irow, icol, frow, fcol);
			}
			openSet.remove(currentNode);
			closedSet.add(currentNode);

			for (int i = 0; i < 8; i++) {
				switch (i) {
				case 0:
					neighborRow = currentNode.getRowNum() - 1;
					neighborCol = currentNode.getColNum();
					break;
				case 1:
					neighborRow = currentNode.getRowNum();
					neighborCol = currentNode.getColNum() - 1;
					break;
				case 2:
					neighborRow = currentNode.getRowNum();
					neighborCol = currentNode.getColNum() + 1;
					break;
				case 3:
					neighborRow = currentNode.getRowNum() + 1;
					neighborCol = currentNode.getColNum();
					break;
				}

				if (isValidCell(neighborRow, neighborCol) && allCells[neighborRow][neighborCol].getColor() == 0) {
					currentNodeNeighbor = allCells[neighborRow][neighborCol];

					if (closedSet.contains(currentNodeNeighbor)) {
						// 1 is distance between currentNode & currentNodeNeighbor
						tentativegScore = gScore[currentNode.getRowNum()][currentNode
								.getColNum()] + 1;
						tentativeIsBetter = false;
						if (!openSet.contains(currentNodeNeighbor)) {
							openSet.add(currentNodeNeighbor);
							hScore[neighborRow][neighborCol] = Math.abs(frow
									- neighborRow)
									+ Math.abs(fcol - neighborCol);
							tentativeIsBetter = true;
						} else if (tentativegScore < gScore[neighborRow][neighborCol]) {
							tentativeIsBetter = true;
						}
						if (tentativeIsBetter == true) {
							allCells[neighborRow][neighborCol].setParentNode(
									currentNode.getRowNum(), currentNode
											.getColNum());
							gScore[neighborRow][neighborCol] = tentativegScore;
							fScore[neighborRow][neighborCol] = gScore[neighborRow][neighborCol]
									+ hScore[neighborRow][neighborCol];
						}
					}
				}
			}
		}
		return new ArrayList<OrderedCoordinatePair>();
	}

	ArrayList<OrderedCoordinatePair> reconstructPath(int initialRow,
			int initialCol, int finalRow, int finalCol) {
		int currentRow = finalRow;
		int currentCol = finalCol;

		int tempRow = currentRow;
		int tempCol = currentCol;

		while (currentRow != initialRow && currentCol != initialCol) {
			shortestPath.add(allCells[currentRow][currentCol]);
			tempRow = currentRow;
			tempCol = currentCol;

			currentRow = allCells[tempRow][tempCol].getRowNum();
			currentCol = allCells[tempRow][tempCol].getColNum();
		}

		return shortestPath;
	}