public boolean hit() {		// hit其实是对地板的撞击检测
		if (yard.blocks[bl1.row + 1][bl1.col] == true ||
				yard.blocks[bl2.row + 1][bl2.col] == true ||
				yard.blocks[bl3.row + 1][bl3.col] == true ||
				yard.blocks[bl4.row + 1][bl4.col] == true )
			return true;
		else
			return false;
	}