public boolean isCollisionUpDown(int a_x, int a_y)
    {
        int consUpDown = 1, consRightLeft = 1; //we suppose there is collision in (a_x, a_y)
        if(a_y+1 < m_mapChar[a_x].length)
        {
            consUpDown += isObstacle(m_mapChar[a_x][a_y+1])? 1:0;
        }
        if(a_y-1 >= 0)
        {
            consUpDown += isObstacle(m_mapChar[a_x][a_y-1])? 1:0;
        }

        if(a_x+1 < m_mapChar.length)
        {
            consRightLeft += isObstacle(m_mapChar[a_x+1][a_y])? 1:0;
        }
        if(a_x-1 >= 0)
        {
            consRightLeft += isObstacle(m_mapChar[a_x-1][a_y])? 1:0;
        }

        return consUpDown>consRightLeft;
    }