Figure 22-2. A simple Java class used to delete a file

Hey, that was easy! Of course, you didn't watch me fumble around with Java for a day, getting over the nuisance of minor syntax errors, the agony of a case-sensitive language, and the confusion setting the CLASSPATH. I'll leave all that to your imagination—and your own day of fumbling!

22.3.3 Compiling and Loading into Oracle

Now that my class is written, I need to compile. To do this I open an MS-DOS session on a Windows platform, change to the d:\Java directory (or wherever the Sun JDK is installed on your machine), and compile the class:

D:\Java> javac JDelete.java

Now that it's compiled, I realize that it would make an awful lot of sense to test the function before I stick it inside Oracle and try it from PL/SQL. You are always better off building and testing incrementally. Java gives us an easy way to do this: the main method. If you provide a void method (procedure) called main in your class—and give it the right parameter list—you can then call the class, and this code will execute.

The main method is one example of how Java treats certain elements in a special way if they have the right signature. Another example is the toString method. If you add a method with this name to your class, it will automatically be called to display your custom description of the object. This is especially useful when your object consists of many elements that make sense only when presented a certain way, or that otherwise require formatting to be readable.

So let's add a simple main method (shown in bold) toJDelete:

public class JDelete {

public static int delete ...

public static void main (String args[]) {

System.out.println (

delete (args[0])

);

}

}

In other words, you call delete for the first value passed to the class and then display the value being returned. Now I will recompile the class and run it (this example is taken from a DOS window):

D:\Java>javac JDelete.java

D:\Java>java JDelete c:\temp\te_employee.pks

1

D:\Java>java JDelete c:\temp\te_employee.pks

0

Notice that the first time I run the main method it displays 1 (TRUE), indicating that the file was deleted. So it will come as no surprise that when I run the same command again, main displays 0. It couldn't delete a file that had already been deleted.

That didn't take too much work or know-how, did it?

In another demonstration of the superiority of Java over PL/SQL, please note that while you have to type 20 characters in PL/SQL to display output (DBMS_OUTPUT.PUT_LINE), you needn't type any more than 18 characters in Java (System.out.println). Give us a break, you language designers! Though Alex Romankeuich, one of our technical reviewers, notes that if you declare "private static final PrintStream o = System.out;" at the beginning of the class, you can then display output in the class with the command "o.println"—only 9 characters in all!

Now that my class compiles and I have verified that the delete method works, I will load it into the SCOTT schema of the Oracle database using the loadjava command:

D:\Java>loadjava -user scott/tiger -oci8 -resolve JDelete.class

I can even verify that the class is loaded by querying the contents of the USER_OBJECTS data dictionary via a utility I'll introduce later in this chapter:

SQL> exec myjava.showobjects

Object Name Object Type Status Timestamp

---------------------------------------------------

Hello JAVA CLASS VALID 1999-05-19:16:42

JDelete JAVA CLASS VALID 1999-06-07:13:20

JFile2 JAVA CLASS VALID 1999-05-26:17:07

JFile3 JAVA CLASS VALID 1999-05-27:12:53

That takes care of all the Java-specific steps, which means that it's time to return to the cozy world of PL/SQL.