public enum Direction {
    NORTH(0,-1),
    NORTHEAST(1,-1),
    EAST(1,0),
    SOUTHEAST(1,1),
    SOUTH(0,1),
    SOUTHWEST(-1,1),
    WEST(-1,0),
    NORTHWEST(-1,-1);

    int x;
    int y;

    Direction(int x, int y)
    {
        this.x = x;
        this.y = y;
    }

    public Direction getOpposite()
    {
        return Direction.values()[(this.ordinal()+4)%8]
    }
}

...

public bool hasCharInDirection(char[][] minefield, char target, int x, int y, Direction dir)
{
    int newx = x + dir.x;
    int newy = y + dir.y;
    if (0 <= newy && newy < minefield.length
     && 0 <= newx && newx < minefield[0].length)
    {
        return minefield[newy][newx] == target;
    }
    return false;
}

...

int mineCount = 0;
for (Direction dir : Direction.values())
{
    mineCount += hasCharInDirection(minefield, '*', x, y, dir) ? 1 : 0;
}