This sample illustrates the object type inheritance
support in Oracle9i JDBC Drivers.
Object-type inheritance feature allows to create a new object type
by extending another object type. The new object type is then a
subtype of the object type from which it extends. The subtype automatically
inherits all the attributes and methods defined in the supertype.
The subtype can add attributes, methods and overload or override
methods inherited from the supertype.
Sample Application Scenario
Consider a Residential University in which all persons are
categorized under Students, Teachers and Part-time Students. This
model has four new object types. Person is a super type and its attributes
are common to all persons. It has two sub types Student and Teacher.
Teacher has additional attributes like courses taught, Salary and
date of joining. Student has additional attributes like courses taken,
grade and year of completion. A Part-time student is a sub-type of
Student with some additional attributes such as No of hours, Start
time and Batch code. All the sub-types have overridden methods for
setting and retrieving the attributes.
In this sample the user can View/Edit person
details.For viewing person details, the overridden getpersondetails()
method is called which returns a String representation of the Object
attributes. For updating person details, the overridden setpersondetails()
method is called, which sets the attributes and internally calls the
setaddress() method for setting the address.
This sample illustrates
Method Overloading: Here the method getPersonDetails()
is overloaded. When invoked on Student Object, this method returns
the courses taken, grade etc information apart from Name and Address
information. When invoked on Teacher Object, this method returns
the information like courses taught, Salary, Department apart
from Name and Address.
Dynamic Method Dispatching: This is nothing but run-time
polymorphism. When you invoke an overridden method, the implementation
of the methods is searched in the current type and then upwards
in the type hierarchy (type and super types of the type). In other
words, if setAddress() is invoked from a Student Object, then
method in Person Object is invoked, since there is no implementation
of setAddress() in Student Object, but if the same method is called
from a Teacher object the implementation in the Teacher Object
is called.
Substituting Types in a Type Hierarchy: A base object type
can hold any of its sub-types object i.e. Person is the base type
and it can hold either a Student, Teacher or a Part-time Student
object which are sub-types of Person.
Here is the code usage for using ObjectTypeInheritance
feature of Oracle9i JDBC drivers.
You can find more details of the code in ObjectTypeInheritanceSample.java
file under src\oracle\otnsamples\oracle9ijdbc\objecttypeinheritance
folder. Look into Description of Sample
Files section for folder and file details.
public class ObjectTypeInheritanceSample
{
.......................
/**
* This method gets the Id of the person who has been
selected in the JTable
* and retrieves the corresponding person object from
the PersonDetails table.
*/ public Person getPersonDetails(String p_id) { Person personObj = null;
PreparedStatement pstmt = null;
..........................
pstmt = m_conn.prepareStatement("
SELECT p.person "+
" FROM PersonDetails p "+
" WHERE p.person.Id=? ");
..........................
// select the person object from
PersonDetails table
rset = pstmt.executeQuery ();
..........................
// Retrieve the
object and assign it to a person object, a person
object
// can hold all its sub-type objects
(substitutability) personObj = (Person)rset.getObject(1);
...........................................
}
/**
* This method retrieves the objects from the PersonDetails
table and displays
* Id, Name and Object type of objects in a JTable.
*/
private void displayPersonDetails() {
Person personObj;
.....................
//
Retrieve the objects from PersonDetails table
rset = stmt.executeQuery("SELECT
p.person FROM PersonDetails p");
// Retrieve the object and assign
it to a Person object, a Person object
// can hold all its sub-type objects
(substitutability) personObj = (Person)rset.getObject(1);
//
An object of Part-time Student will also be an instance
of Student,
// since Part-time Student is a
sub-type of student. Hence the retrieved
// object is first compared with
a partimestudent and then with a
// student(a student object will
not be an instance of Part-time Student)
// If the retrieved object is a
Part-timeStudent if(personObj instanceof ParttimeStudent)
objType="
P ";
// If the retrieved object is a
student else if(personObj instanceof
Student) objType="
S ";
.....................
// Get the Id Id = personObj.getId(); .....................
Oracle9i JDeveloper (
Note: Oracle9i JDeveloper
is Oracle's Visual Java Development Tool and can be downloaded
from here )
or JDK1.2.x or above This can be downloaded from here .
Oracle9i Database or higher
running SQL*Net TCP/IP listener. This can be downloaded from here .
Oracle9i v9.0.1 JDBC Drivers
for use with JDK 1.2.x , downloadable from OTN
site.
If Oracle9i client is already
installed on your system then this driver need not be downloaded
separately.
Note:You will find
jar.exe in <JAVA_HOME>\bin. Ensure <JAVA_HOME>\bin
is present in your system path.
For setting up environment variables in different platforms,
please refer environment set up
readme document.
This creates a folder ObjectTypeInheritanceSample with all
the source files.
Edit ObjectTypeInheritanceSample\Connection.properties file in your favorite editor. Change the HostName,
Port, SID, UserName and Password
to connect to your own database.
HostName
=
localhost
SID
=
ORCL
Port
=
1521
UserName
=
scott
Password
=
tiger
NOTE: The Custom java classes which are generated
by the JPublisher and included along with the sample use "SCOTT"
schema. In case you use some other database user, then you need to
generate the Custom java classes using JPublisher utility. Run the
SQL script and then follow the instructions
for generating custom java classes.
To create the required tables and populate it with sample data,
run SQL*Plus or Server Manager, connect to your test database
as scott/tiger and execute the install.sql script as shown below.
SQL> @<SAMPLE_HOME>\sql\install.sql
This section describes
steps to run the application from console using JDK(version 1.2 or above)
for Windows and Redhat Linux Advanced Server version 2.1. This application
can be run either manually or using a script file.
Run the application
using script file :
Make sure that the environment variables[<JAVA_HOME>
and <ORACLE_HOME>] have been set before proceeding futher. For
more information on how to setup these environment variables in different
platforms, please refer environment set up
readme document
If JDK 1.4 is used, then ojdbc14.jar(downloadable
from OTN) must be used. For all other JDK versions, classes12.jar
must be used.
Now the sample application can be directly
run by just executing the script file: run.bat/run.sh
from the command prompt, from ObjectTypeInheritanceSample directory.
Execute the script file in Windows as follows D:\ObjectTypeInheritanceSample\run
For Redhat Linux Advanced Server version
2.1 environment, execute the script file as follows: $sh run.sh
Running the application
manually:
Set CLASSPATH to include Oracle9i JDBC Driver file: classes12.jar or classes12.zip or ojdbc14.jar
. Also set the CLASSPATH to include Oracle9i SQLJ driver
files: translator.jar and runtime12ee.jar. For more information on how
to setup environment variables in different platforms, please refer environment set up readme document
Also addObjectTypeInheritanceSample directory whereConnection.properties exists and the current directory to the CLASSPATH
Make sure that <JAVA_HOME>\bin is
in the path. Also make sure that <ORACLE_HOME>\bin
is in the classpathwhich contains sqlj.exe. Note :If JDK 1.4 is used, then ojdbc14.jar(downloadable
from OTN) must be used. For all other JDK versions, classes12.jar
must be used.
From the directory ObjectTypeInheritanceSample\src\oracle\otnsamples\oracle9ijdbc\objecttypeinheritance, compile
all the java files using sqlj:
Example: sqlj -d=. -status -ser2class *.sqlj
*.java
Run the class file using java from
ObjectTypeInheritanceSample\src\oracle\otnsamples\oracle9ijdbc\objecttypeinheritance directory
Example:
java oracle.otnsamples.oracle9ijdbc.objecttypeinheritance.ObjectTypeInheritanceSample
The directory structure of the deliverable ObjectTypeInheritanceSample.jar will be as shown below.
ObjectTypeInheritanceSample is the top level
directory.
Directory
Files
Description
ObjectTypeInheritanceSample
ObjectTypeInheritanceSample.jws
The Oracle9i JDeveloper workspace
file
ObjectTypeInheritanceSample.jpr
The Oracle9i JDeveloper project
file
connection.properties
This file has the details of the database connection parameters
run.bat
The batch file to compile and run the sample in Windows environment
run.sh
The shell script file to compile and run the sample in Linux environment
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