Running Code for a GUI Applet

On my first attempt at running the modified Applet from within a web page, I was delighted to observe that it worked. I then noticed the following lines of code:

/**
* These are implementation variables
*/
boolean dbDEBUG = false;
boolean mathDEBUG = false;
boolean LIVE = false;

I had very cunningly (in my opinion) put in a safety check. By default, no attempt is made to attempt to connect to a database, and the applet just runs without it. So I had not been so clever with the coding change as I initially thought. The applet had run, but without attempting to implement the new connection code. So with great trepidation I changed both boolean LIVE and boolean dbDEBUG to true, recompiled, and tried again.

Again to my delight, the applet opened, and there was even a debug message saying:

starting... driver succeeds...

However my joy subsided when I clicked the "Click to begin" button, entered an answer clicked "Check Answer" and the debug field read:

SQLException: nullSQLException: null.

The original text file class, used to create the database in Derby, included some code to populate a few lines. On reflection, I could see why I included this, and that perhaps it would have been a good idea to run it first.

So I modified the class to connect to MySQL, renamed it to ItemdbTest, and compiled it. I also modified another text file/command line class, ItemdbQuery, which runs a simple query and displays the table contents. The SQL for the insert was:

"INSERT INTO Items " +
"(Partid, OpCode, Itemdet, Raw, Rate) " +
"VALUES (1, 1, '1+1=', 1, 1), " +
"(1, 1, '2+2=', 1, 1), " +
"(1, 1, '3+3=', 1, 1)";

That ran fine. The SQL for the simple query was:

"SELECT * FROM Items"

and the output was:

try connection
connection succeeds
try query
1 1 1 1+1= 1 1
2 1 1 2+2= 1 1
3 1 1 3+3= 1 1
query succeeds
disconnection succeeds

Now the SQL used here is supposed to reflect that in the Applet, so it was strange that the Applet is falling over, when a similar command from the command line was working.

On further investigation, the answer lay on the What Applets Can and Cannot Do page in the Java Tutorial. I remember when I was first trying to use the Derby embedded driver, an applet can't make changes on the local machine. So I shall have to set up IIS on either this or another machine, set MySQL to accept outside connections, and start again.

Comments

Post a Comment

Popular posts from this blog

A few notes on JavaScript

I am one the 99% of the world who has long nursed the misconception that JavaScript has something to do with Java. And why not? The name sort of implies it. It was only after I searched without success on the Java Tutorial site for some mention of JavaScript that I stumbled across the knowledge that JavaScript was in fact developed by Netscape, under the name LiveScript. Armed with that knowledge, it is not surprising to find the best reference information on Mozilla site. According to Wikipedia , the nonsensical name choice had something to do with Netscape wanting to cash in on the popularity and cachet of Java, and Sun wanting support for Java technology in the then popular Netscape browser. For a while only the Netscape family of browsers supported JavaScript. Microsoft later produced what it calls JScript to run in its browser. JScript is similar but not identical to Javascript. According to Foldoc JavaScript runs a hundred times slower than C , and ten
Read more

Forum Comments on Java Applets

It is so long since I last posted on the once was Sun/Java now is Oracle developer forum my account seems to have been ditched. While I wait to have it resurrected I've done a little searching in the Java Database Connectivity (JDBC) forum using the search term "Applet". My first search, using the default 3 month period, yielded nothing. No one had posted anything about or even mentioned Applets in the last three months. So either they are very easy to use and work very well, so hardly anyone has any problems with them, or maybe ... not very many people use them at all. My stomach was beginning to churn a bit, when I extended the search period to the current year - and with good reason. Somebody, a little bit like me I think, had written a game in an applet, and wanted to record top scores in a database. He described his connection problem in this thread , and the first reply began: Doing JDBC calls from an Applet is such a bad idea that I am glad y
Read more

Creating a Custom Swing Component

Image
I always return to my blog when I'm stuck, and I'm stuck right now. I want to create a custom Swing component. Specifically, I want something like a JProgressBar , with the following changes: In place of a flat Foreground color, I want a rainbow spectrum, showing only the red range for low Values, and the whole spectrum for values close to the Maximum value; Instead of a rectangular box, I want the progress "bar" to take the shape of a normal, or Gaussian, distribution curve; I want progress to be displayed by the area under the curve, rather than by a simple linear scale along the x axis. It's not that there isn't stuff out there. I have five tabs open in my browser, specifically addressing the creation of custom components in Swing, as well as the source code for the JProgressBar . It is that, like everything to do with Java, it is bloody difficult to read. I shall begin from the horse's mouth as it were, with an article on the Java
Read more