gistfile1.txt

interface BTPrinter
{
	void printAt(int top, int left, String message);
	//add more methods here
	void selectFont(String font);
	void cutThePaper();
}


class ZebraPrinter implements BTPrinter
{
	public void printAt(int top, int left, String message)
	{
		//it is just a sample assumption you need to send "top, left:message"
		socket.send(top + ", " + left + ":" + message);
	}
	public void selectFont(String font)
	{
		//we do nothing this printer do not supports fonts
	}
	public void cutThePaper()
	{
		socket.send("cut");
	}
	
}


class BixolonPrinter implements BTPrinter
{
	public void printAt(int top, int left, String message)
	{
		//it is just a sample assumption you need to send "%ttop%lleft%mmessage"
		socket.send("%t" + top + "%l" + left + "%m" + message);
	}
	
	public void selectFont(String font)
	{
		socket.send("%f" + font);
	}
	
	public void cutThePaper()
	{
		socket.send("%c");
	}
}

class BTPrinterFactory
{
	public static public BTPrinter createInstanceFromId(String id)
	{
		if(id.equals("ZebraPrinter"))
			return new ZebraPrinter();
		if(id.equals("BixolonPrinter"))
			return new BixolonPrinter();
		throw new UnknowDeviceException();
	}
}

usage:

String id = obtainIdFromPrinter();
BTPrinter thePrinterObject = BTPrinterFactory.createInstanceFromId(id);
thePrinterObject.cutThePaper();
thePrinterObject.printAt(10,10, "hello");