1. Electronic Commerce Java (1)
John Wordsworth
Department of Computer Science
The University of Reading
Room 129, Ext 6544
April 2002
3CSG1

2. Lecture objectives
Outline the place of the Java language in E-commerce
Revise the concepts of object-oriented programming
Describe the structure of a Java class and its parts
Describe the structure of a Java application, and the way it uses objects
Explain how Java implements inheritance
April 2002
3CSG1

3. What is Java
An object-oriented programming language invented by Sun Microsystems
A collection of classes that model useful objects: windows, buttons, text areas, files, databases …
A language for developing applications that can be executed on many platforms:
Write Java source code
Compile to Java bytecodes (javac)
Execute under the control of the Java Virtual Machine (java)
April 2002
3CSG1

4. Java in e-commerce Client programming with applets:
Classes for setting up and controlling the graphical user interface
Server programming with servlets:
Classes for managing the interface with tier 1 (JSPs)
Classes for managing the interface with tier 3 (EJBs)
April 2002
3CSG1

5. An object-oriented language
Object - an instance of a class:
variables
methods
Message - executing a method:
destination object (class)
parameters
Class - a blueprint for objects:
class variable (static) and class method (static)
instance variable and instance method
constructor
inheritance
Interface - a collection of methods
April 2002
3CSG1

6. An interface for a simple bank account
public interface AccountIf {
void deposit (int amt);
void withdraw (int amt);
void showBal; }
April 2002
3CSG1

7. A class for a simple bank account
public class Account implements AccountIf {
private String sortcode, acctno;
private int balance;
Account (String sc, String an)
{ sortcode = new String (sc);
acctno = new String (an);balance = 0;}
public void deposit (int amt)
{ balance = balance + amt; }
public void withdraw (int amt)
{ balance = balance – amt;}
public void showBal { System.out.println
( “Sort code “+sortcode+” Acct number “+acctno=“ Balance “+balance); }
April 2002
3CSG1

8. A program to use a bank account
public class AccountMain {
public static void main (String [] args)
{ Account ac1 = new Account ("304050", " ");
ac1.showBal();
ac1.deposit(500);
ac1.withdraw(575); }
April 2002
3CSG1

9. A bit of inheritance public class DAccount extends Account
{ DAccount (String sc, String an, int opening) { super (sc, an); balance = opening;}
public void withdraw (int amt)
{ if (amt < balance)
{ balance = balance - amt; }
else
{ System.out.println ( "Withdrawal not allowed"); } }
April 2002
3CSG1

10. A program to use a deposit account
public class DAccountMain {
public static void main (String [] args)
{ DAccount ac2 = new DAccount ("304050", " “, 1000);
ac1.showBal();
ac1.withdraw(500); }
April 2002
3CSG1

11. Sample output Sort code 405060 Account number 98765432 Balance 1000
Withdrawal not allowed
April 2002
3CSG1

12. Key points
Java is an object-oriented language for writing portable applications.
Java has classes that support the construction of programs to run in Tier 1 (applets) and Tier 2 (servlets) of an e-commerce system.
Java classes have a regular structure that can be adapted to writing object-oriented applications, classes, and objects.
April 2002
3CSG1