1. IT258 Foundation of Programming Using Java
Unit 2 Seminar :
(Chapter 1 )
Instructor : Vladimir Gubanov, PhD

2. they will be each Thursday , from 9 PM to 10 PM EST
A reminder:
Our Seminars :
they will be each Thursday , from 9 PM to 10 PM EST
My Office Hours :
Mondays, 7PM to 8PM
Saturdays, 9AM to 10 AM My

3. Java Programming, Fifth Edition
Chapter One:
Creating Your First Java Classes

4. Objectives Object-oriented programming concepts Learn about Java
Analyze a Java application that uses console output
Save, compile, run, and modify a Java application
Create a Java application using GUI output
Java Programming, Fifth Edition

5. Object-Oriented Programming Concepts
Procedural programming
Sets of operations executed in sequence
Variables hold values
Procedures group operations in logical units
Object-oriented programs
Create classes first
Create objects from classes when a functionality of the class needs to be used
Object-oriented programming includes:
Encapsulation
Inheritance
Polymorphism
Java Programming, Fifth Edition

6. Understanding Objects and Classes
Made up of attributes, methods, events
Attributes
Characteristics that define object
Value of attributes is object’s state
Class
Describes objects with common properties
Definition – template for objects
Instance of a class – an object to use
Java Programming, Fifth Edition

7. OBJECT Represents something you would find in the “real-world”
Objects can be described by their attributes(properties) and behaviors(methods)
In Java, an object is represented by a software module, which contains a collection of related data and procedures
Object: Car

8. PROPERTY (or field) Attribute which describes the object:
In Java, a property is represented by a variable associated with the object
Property: Color
Make
Year
VIN

9. METHOD Behavior of the object or what the object can do
In Java, a method is represented by a public subroutine or function related to the object
Method: Start
Accelerate
Turn Left
Stop

10. STATE
The collection of an object’s property values determine its state
The object’s state can affect its behavior
Object: Car
Property: GasolineLevel
OilLevel
Speed
State

11. CLASS A category of objects – “abstraction”
Template for the object, also called “factory”
Allows multiple objects to have common methods and properties
An object is an “instance” of a class
Objects:
VIN:
Class: Car
VIN:
VIN:

12. INTERFACE
The set of public methods and properties which are available to access or manipulate the object
An object may have many interfaces
Object: Car
Properties: Color GasolineLevel
Make OilLevel
Model Speed
Year
Methods: Stop Turn Left
Start Turn Right
Accelerate
Interface

13. room window door CLASS : elaborate
A blueprint is the specification of a
House. This blueprint specifies
a house with room, door, and window.
room
There are several means of explaining object-oriented concepts.
Weber chapter 5 (assumes syntax understanding)
Farrel the first few chapters (covers the concepts from a coding perspective and not so much a conceptual one)
The particular faculty member might want to use his/her own methods/analogies for explaining object-oriented concepts and forgo all or parts of this explanation.
window
door

14. class object A class is the specification from which a developer
A blueprint is the
specification from
which a builder
generates houses
class
object
A class is the
specification
from which a
developer
generates objects
Analogies seem to be the easiest way to explain object-oriented principles, but be very careful that the analogy is not misinterpreted.

15. ENCAPSULATION
Hides the internal workings of an object from the rest of the application.
You may change Implementation while interface remains constant
In Java properties and methods are used to get information and perform actions in an application that are hidden within classes:
you do not know how they are implemented , but can use then as “black box”

16. INHERITANCE: Very Important
Ability to reuse functionality in a class.
A base class defines the common functionality:
Subclasses inherit that functionality and may add new functionality
i.e.: A general class of Sport Car is used to create sub-classes of Camaro and FireBird. They have many similar (re-used) features but are different cars, because they have other properties (methods) different.

17. Learning About Java Java Developed by Sun Microsystems
Object-oriented language
Advantages :
Simple, Distributed , Interpreted, Secure
Architecture neutral, Portable, Multithreaded
Can be run on wide variety of computers
Runs on hypothetical computer known as Java virtual machine (JVM)
Java Programming, Fifth Edition

18. Learning About Java (continued)
Can be run on wide variety of computers
Does not execute instructions on computer directly
Runs on hypothetical computer known as Java virtual machine (JVM)
Source code
Programming statements written in high-level programming language
Java Programming, Fifth Edition

19. The Java Virtual Machine – special “basic computer”
Java is platform independent. What this means is that a program written in
Java should be executable in any computer with any chipset.
This is done by means of the Java Virtual Machine (JVM). The JVM interacts with
a computer through bytecode.
Computer
JVM
Program

20. Java Program Types Applets Java applications
Programs embedded in Web page
Java applications
Called Java stand-alone programs
Console applications
Support character output
GUI based applications
Menus
Toolbars
Dialog boxes
Java Programming, Fifth Edition

21. Java Programming Process:
Write a specification for the program (what the program is supposed to do)
Design the program
Choose algorithms and decide how data will be stored , develop pseudocode and/or flowchart
Write the program (Java language, indeed!)
Compile the program (to lower-level language)
Execute the program
Debug the program
Maintenan the program in a workable condition

22. Analyzing a Java Application That Uses Console Output
Even simplest Java application
Involves fair amount of confusing syntax
Goal of the first application :
Print “First Java application” on screen
Java Programming, Fifth Edition

23. Analyzing a Java Application That Uses Console Output :
Java Programming, Fifth Edition

24. Understanding the First Class
Everything used within Java program must be part of a class
Define Java class using any name or identifier
Requirements for identifiers
Must begin with:
Letter of English alphabet
Or non-English letter (such as α or π)
Cannot begin with digit
Java Programming, Fifth Edition

25. Understanding the First Class
Requirements for identifiers
Can only contain:
Letters
Digits
Underscores
Dollar signs
Cannot be Java reserved keyword
Cannot be true, false, or null
Access modifier
Defines how class can be accessed
Java Programming, Fifth Edition

26. Understanding the First Class
Java Programming, Fifth Edition

27. Understanding the Statement That Prints the Output
Java Programming, Fifth Edition

28. Some Illigal in Java Class names
Java Programming, Fifth Edition

29. Understanding the First Class (continued)
Java Programming, Fifth Edition

30. Understanding the main() Method
static
Means method accessible and usable
Even though no objects of class exist
void
Use in main() method header
Indicates main() method does not return value when called
Doesn’t mean main() doesn’t produce output
Java Programming, Fifth Edition

31. Another Java Program: Example.java/*
This is a simple Java program.
Call this file Example.java */
class Example {
//A Java program begins with a call to main().
public static void main(String[] args)
System.out.println("Java drives the Web."); // System.out : console output
} // println() displays the string
} // passed to it
Change .println to Println and compile
Here: Java is case sensitive language!!
a source file : the same name as class with .java extension
comments(ignored by the compiler): single line and multiline
a subroutine is called a method; main() method is the entry point
public: access specifier ; static – can be called before an object is
created from a class ;
void - does not return a value

32. Shell Code – create and use as a template for any class
Do not forget to same in the file AnyClassName.java
Java Programming, Fifth Edition

33. Adding Comments to a Java Class
Types of Java comments
Line comments
Start with two forward slashes (//)
Continue to end of current line
Do not require ending symbol
Block comments
Start with forward slash and asterisk (/*)
End with asterisk and forward slash (*/)
Java Programming, Fifth Edition

34. Saving, Compiling, and Running and Modifying a Java Application
Saving a Java class
Save class in file with exactly same name and.java extension
For public classes
Class name and filename must match exactly
Compiling a Java class
Compile source code into bytecode
Translate bytecode into executable statements
Using Java interpreter
Type javac First.java
Java Programming, Fifth Edition

35. Running a Java Application
Run application from command line
Type java First
Shows application’s output in command window
Class stored in folder named Java on C drive
Java Programming, Fifth Edition

36. Running a Java Application
In order javac and java programs be able to find First.java and First.class files - set up Environmental Path variable
Java Programming, Fifth Edition

37. Modifying a Java Class Modify text file that contains existing class
Save file with changes
Using same filename
Compile class with javac command
Interpret class bytecode and execute class using java command
Java Programming, Fifth Edition

38. Creating a Java Application Using GUI Output
JOptionPane
Produce dialog boxes
Dialog box
GUI object resembling window
Messages placed for display
Package
Group of classes
import statement
Use to access built-in Java class
Java Programming, Fifth Edition

39. Creating a Java Application Using GUI Output
Java Programming, Fifth Edition

40. Correcting Errors First line of error message displays:
Name of file where error found
Line number
Nature of error
Next lines identify:
Symbol
Location
Compile-time error
Compiler detects violation of language rules
Refuses to translate class to machine code
Do not expect miracles : an error message will only approximately indicate where an error is and what it could be – no guarantee that these are 100% correct
Java Programming, Fifth Edition

41. Correcting Errors and Finding Help (continued)
Parsing
Process compiler uses to divide source code into meaningful portions
Logic error
Syntax correct but produces incorrect results when executed
Usually more difficult to find and resolve
Java API
Also called the Java class library
Prewritten Java classes
Java Programming, Fifth Edition

42. You Do It Your first application Adding comments to a class
Modifying a class
Creating a dialog box
Java Programming, Fifth Edition

43. Don’t Do It File’s name must match name of class
Don’t confuse names parentheses, braces, brackets, curly braces, square brackets, and angle brackets
Don’t forget to end a block comment
Don’t forget that Java is case sensitive
End every statement with semicolon
Do not end class or method headers with semicolon
Recompile when making changes
Java Programming, Fifth Edition

44. Summary Computer program
Set of instructions that tells a computer what to do
Object-oriented programs
Classes
Objects
Java virtual machine (JVM)
Standardized hypothetical computer
Everything in a Java program must be part of a class
Java Programming, Fifth Edition

45. Summary (continued) Access modifier
Word that defines circumstances under which class can be accessed
All Java applications must have method named main()
Program comments
Nonexecuting statements
Add to file for documentation
javac
Compile command
Java Programming, Fifth Edition

46. Summary (continued) java JOptionPane Execute command GUI
Provides methods for creating dialogs
Java Programming, Fifth Edition

47. Quiz
True or False: Object-oriented programming is a style of programming in which sets of operations are executed one after another in sequence.
Answer: False
Writing ____ programs involves creating classes, creating objects from those classes, and creating applications.
Answer: object-oriented Answer: False
A(n) ____ of a class is an existing object of a class.
Answer: instance
Programming statements written in a high-level programming language are called ____.
Answer: source code

48. Quiz (cont.) Stand-alone programs are called Java ____.
Answer: applications
Answer: True
True or False: Not all classes have a main() method.
Line comments start with ____.
Answer: two forward slashes (//)

49. Quiz (cont.)
True or False: In Java, if a class is public (that is, if you use the public access modifier before the class name), you must save the class in a file with exactly the same name and a .class extension.
Answer: False and *=
To compile a file named First.java, you type ____ First.java and then press Enter.
Answer: javac
To run the First application from the command line, you type ____ First.
Answer: java

50. Quiz (cont.)
A(n) ____ is a GUI object resembling a window in which you can place messages you want to display.
Answer: dialog box

51. This is the end of our Unit 2 Seminar
Any questions ?