messy.java

  ...
  public Game nextTick() {
    HashMap<Cell, Integer> updateMap = new HashMap<Cell, Integer>();
    for (Cell livingCell : this.cells) {
      for (Cell neighbouringCell : livingCell.neighbours()) {
        int currentCount = updateMap.getOrDefault(neighbouringCell, 0);
        currentCount++;
        updateMap.put(neighbouringCell, currentCount);
      }
    }

    HashSet<Cell> nextCells = new HashSet<>();
    for (HashMap.Entry<Cell, Integer> entry : updateMap.entrySet()) {
      Cell currentCell = entry.getKey();
      int previousNeighbourCount = entry.getValue();

      if (previousNeighbourCount == 2 && this.cells.contains(currentCell)) {
        nextCells.add(currentCell);
      }

      if (previousNeighbourCount == 3) {
        nextCells.add(currentCell);
      }
    }

    boolean needToExpandDown = false;
    for (int col = this.colLowerBound; col <= this.colUpperBound; col++) {
      Cell outsideLowerBoundCell = new Cell(this.rowUpperBound + 1, col);
      if (nextCells.contains(outsideLowerBoundCell)) {
        needToExpandDown = true;
      }
    }

    boolean needToExpandRight = false;
    for (int row = this.rowLowerBound; row <= this.rowUpperBound; row++) {
      Cell outsideRightBoundCell = new Cell(row, colUpperBound + 1);
      if (nextCells.contains(outsideRightBoundCell)) {
        needToExpandRight = true;
      }
    }

    boolean needToExpandUp = false;
    for (int col = this.colLowerBound; col <= this.colUpperBound; col++) {
      Cell outsideUpBoundCell = new Cell(this.rowLowerBound - 1, col);
      if (nextCells.contains(outsideUpBoundCell)) {
        needToExpandUp = true;
      }
    }

    boolean needToExpandLeft = false;
    for (int row = this.rowLowerBound; row <= this.rowUpperBound; row++) {
      Cell outsideLeftBoundCell = new Cell(row, colLowerBound - 1);
      if (nextCells.contains(outsideLeftBoundCell)) {
        needToExpandLeft = true;
      }
    }

    Game updatedGame = new Game(this.rowUpperBound + 1, this.colUpperBound + 1);
    if (needToExpandDown) {
      updatedGame.expandDown();
    }
    if (needToExpandRight) {
      updatedGame.expandRight();
    }
    if (needToExpandUp) {
      updatedGame.expandUp();
    }
    if (needToExpandLeft){
      updatedGame.expandLeft();
    }

    for (Cell cell : nextCells) {
      updatedGame.setCellAlive(cell);
    }

    return updatedGame;
  }
  
  ...