public HydraShot(int ox,int oy,int sx,int sy,Tank tk)
	{
		super(ox,oy,sx,sy,tk);
		this.shotPower=1;
		this.shotRadius=8;//????????????????????????????????????
		this.shotSpeed=13;
		this.oldx=sx;
		this.oldy=sy;
		this.lengthX=shotSpeed*(sx-ox)/(int)Math.hypot(sx-ox,sy-oy);// һ ʲô˼أɢǸmathĺʲô˼һ
		this.lengthY=shotSpeed*(sy-oy)/(int)Math.hypot(sx-ox,sy-oy);
	}