Oracle Java

By Mike Ault

JAVA is an interpreted, platform independent language, was only recently introduced to the computing world. In a few short years it has risen from total obscurity (indeed, non-existence) to a pre-eminent position in the hierarchy of programming languages. This book is not intended as a primer for JAVA, we will examine a few examples using JDBC (JAVA Database Connectivity) and JSQL (An Alpha release of the Oracle PRO*JAVA product offering) against an Oracle8 database. JDK1.1.4, JDBC and JSQL are all available via the Internet.

JAVA owes its platform independence to the fact that it is interpreted and not compiled. Essentially the machine level code for a JAVA script (JAVA Bytecode) is not generated until runtime so the script is downloaded from the web to the local machine. This means that as long as a JAVA interpreter has been written for an operating system your users are on,  the JAVA applet that you write on your PC will run on it. This is synonymous to the language BASIC in  the early days of programming.

One has to wonder that if machines would have been as fast back in the early days of BASIC, making interpreted languages possible for use in production level systems, would other languages such as FORTRAN, COBOL and even C been pursued as readily?

JAVA was initially built to be a toolkit language for small device programming (i.e. that JAVA enabled cappuccino machine). This meant that it had to be highly portable, hence it's emergance as a language of choice for web applications. Now, extensions such as JDBC ( JAVA Database Connectivity - a take off on ODBC - Open Database Connectivity) and now JSQL (JAVA SQL) places JAVA firmly as a prime candidate for use in company intranet databases and for WEB databases as the language to use for your interface between HTML pages and the database servers.

Of course, JAVA with the various extensions such as JDBC and JSQL, can also be used as a stand alone language with or without HTML wrapping. JAVAScript also will play a part in development of the entire JAVA paradigm.

Due to security features of JAVA, if it is used to access databases on other servers, it is not allowed to rely on such objects as external shared libraries such as DLLs. Therefore there are two modes for use of the JDBC component, the first relies on external ODBC/JDBC communication libraries. The second, known as a "thin" connection, uses internalized drivers allowing it to access remote databases.

Due to JAVA being in its youth, it is still undergoing many changes and improvements. This can sometimes lead to difficulties as classes are depreciated (this means made obsolete, dropped or changed) the WWW.JAVASOFT.COM  web page will provide the latest copy of the JDK (JAVA Developers Kit), at least until the language is officially "mature".

The version provided on the enclosed CD-ROM is JDK1.1.4, additionally, the JDK1.0 version is also provided in case your system browsers can't support the newer version. I suggest obtaining the latest copies of the various browsers and be sure that they are JAVA compliant or the examples in this book may not function without modification (beyond username, password and connection data).

The JDBC and JSQL extensions are available from the WWW.ORACLE.COM webpage and if you read this after mid-1998 I suggest downloading the latest copies from there.

JAVA is case sensitive. This case sensitivity means if a method is named DBATempSelect that is how it must be referred to from now on. This seems to be a carry over from JAVAs SUN-UNIX  beginnings. I know I would never have multiple objects with only a capital letter or so difference between their names, how about you? If a method, class or variable name is shown a specific way then it must be used that way, remember this fact when dealing with the JAVA documentation.

I utilized over $300.00 worth of after market books. You see, JAVA is young enough that there is no one reference that provides insight into use of JAVA with databases, use of JAVA with images and use of JAVA, JDBC and JSQL, each book seems to have pieces of the puzzle, but not the complete picture.

In spite of all of these references I still had to email a couple of other Coriolis authors with a question about a problem that the JAVA virtual machine beat me up over for a couple of days. It is critical that you use the most current version of the JDK (JAVA Developers Kit) and the class libraries and that your references are as current as possible. One problem that you will encounter if you use outdated libraries is called "deprecation".

Deprecation is the process by which old versions of JAVA classes are marked so that the JAVA compiler warns you that they are no longer actively supported. While many books tell you about this, they don't tell you how to fix the problem when it happens.

In JAVA There are already several major classes with many subclasses beneath them. Some examples of the major classes are : awt, io, lang, applet, net and utl. Some examples (from the awt superclass) of subclasses are: peer, image, graphics, component just to name a few.

The section of the LeMay book on the awt package of classes takes 165 pages to cover just the basics of the package definition. Of course each class and subclass may have many methods (usually 8-10) including constructor methods and, since JAVA supports inheritance any subclass inherits behaviors from the superclass it is a part of. All of this inheritance can lead to great confusion when you are trying to find out exactly how to make an instance of class X perform operation Y.