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Preston_5564C02.fm Page 42 Wednesday, September 14, 2005 5:42 AM

42 CHAPTER 2 ■ SERIAL COMMUNICATION

Code Objective

The objective for this example is to simplify communication for my robot by modeling a Stamp
program in Java.

Code Discussion
The first interface I’ll create will be called JController. This interface will have three execute()
methods and one close() method.
The only difference between the two execute methods will be the return type. In execute(),
the return type will be a string. This will call the readString() method from the JSerialPort. In
execute2(), the return type will be a byte[]. This will call the read() method from the JSerialPort.
(See Example 2-11.)

Example 2-11. JController.java Interface
package com.scottpreston.javarobot.chapter2;

public interface JController {

public String execute(byte[] cmd, int delay) throws Exception;
public byte[] execute2(byte[] cmd, int delay) throws Exception;
public void close();
}
Next, I’ll write the implementation for the interface defined in the preceding example.
As I began writing implementation classes for the Javelin Stamp, and six versions of the BASIC
Stamp, I found myself repeating a lot of the same calls to the execute methods. So, rather than
writing them seven times, I decided to create a master controller that would implement the
functionality of all of them. It will also be able to handle any new controllers that might come
up in later chapters. I’ll call this class Controller, and so that the actual implementation classes
are created, I will make it generic.
This class has a single field, serialPort of type JSerialPort. The constructor of this class will
take the JSerialPort interface so that it can use either the WebSerialClient or the StandardSeri-
alPort. I also set the DTR to false since none of the controllers I use will use this, and for the
Stamp Carrier Boards having this set to true will put the Stamp into program mode.
The first method, execute(), will return a string. The first thing that is checked for is the
instance of the JSerialPort. If it’s of type WebSerialClient, then I want to put the delay in the
serial port on the web server. This is due to a timing lag between the executing machine and the
web server connection. I set the maximum delay in the WebSerialClient class and if the delay is
less than or equal to this number, the delay will be set in the WebSerialClient; otherwise, I will
call Utils.pause() and make two calls to the client. Also, in both cases I need to check to see if
the delay is zero. If that’s the case, I don’t want to ready anything; I just want to write. (See
Example 2-12.)