1. Yanal Alahmad Yanal.tg@gmail.com
Java Workshop
Yanal Alahmad

2. Deitel&Deitel [ Java How to Program, 9th ]

3. First Program Every Java program consists of at least one class
A class is a blueprint from which individual objects are created
class is a keyword (reserved word)
By convention, class name begin with a capital letter
A class name is an identifier
Identifier: a series of characters consisting of letters, digits, underscores (_) and dollar signs ($) that does not begin with a digit and does not contain spaces
Java is case sensitive—uppercase and lowercase letters are distinct

4. First Program
For now: every class we define begins with the public keyword
public class must be defined in file with the same name of the class .java extension
Java class declarations normally contain one or more methods
For a Java application, one of the methods must be called main() which JVM calls automatically
public static void main(String args[])
Java program processing starts from the main() method which is a mandatory part of every Java program
void return nothing

5. Example for Student Class
public class Student {
int id;
String firstName;
String lastName
double gpa;
public double getGPA() { }
public void register(int id)

6. First Program
The System.out object is known as the standard output object
System.out.println method takes string as argument and display it on the command window
Every Statement in java ends with semicolon ;
Comments in Java
End-of-line comment //
Multiple lines comment /* …… */
Difference between System.out.print() and System.out.println()

7. Escape Character The backslash (\) is an escape character \n: new line
\t: horizontal tab
\\: print \
\”: print “

8. printf() Displays formatted data
System.out.printf( "%s\n%s\n","Welcome to", "Java Programming!" );
Arguments are separated in a comma-separated list

9. Adding Integers
A great strength of Java is its rich set of predefined classes that you can reuse
These classes are grouped into packages
import declaration that helps the compiler locate a class
Package: java.util
Class: Scanner

10. Variables
A variable is a location in the computer’s memory where a value can be stored for use later in a program
All Java variables must be declared with a name and a type before they can be used
Other types of data include float and double, for holding real numbers
and char, for holding character data
String holds set of characters
The types int, float, double, boolean and char are called primitive types
Note they are keywords and must appear in all lowercase
Several variables of the same type may be declared in a single declaration with the variable names separated by commas
int number1, number2, sum;

11. Object Every thing around us can be an object
Cars
Humans
Cats
Each object has a state and behavior

12. Adding Integers Prompt the user for the input
Note: class System is part of package java.lang
Note: By default, package java.lang is imported in every Java program
Scanner object nextInt() method to obtain an integer from the user at the keyboard
assignment operator = is called a binary operator it has two operands
Portions of statements that contain calculations are called expressions

13. Deitel&Deitel [ Java How to Program, 9th ]
Arithmetic Operators
Deitel&Deitel [ Java How to Program, 9th ]

14. Deitel&Deitel [ Java How to Program, 9th ]
Relational Operators
A condition is an expression that can be true or false
Deitel&Deitel [ Java How to Program, 9th ]

15. Declare Class and Instantiating an Object of a Class
Recall that main is a special method that’s always called automatically by the Java Virtual Machine (JVM) when you execute an application
Method declared as public to indicate that the method is
“available to the public” and can be called from any other class
Return type: specifies the type of data the method returns to its caller after performing its task.
Name of the method
Parameters: method can take empty parameters
Method header: access modifier + return type + method name + parameters including the parentheses

16. Declare Class and Instantiating an Object of a Class
The body of a method contains one or more statements that perform the method’s task
Class GradeBook is not an application because it does not contain main()
static method is special, because you can call it without first creating an object of the class in which the method is declared
Keyword new creates a new object of the class specified to the right of the keyword
Call the method objectName.methodName()

17. Declaring a Method with a Parameter
public void displayMessage(String coursName) {
System.out.println( "Welcome to the Grade Book!" ); }
Scanner input = new Scanner( System.in );
GradeBook myGradeBook = new GradeBook();
System.out.println( "Please enter the course name:" );
String nameOfCourse = input.nextLine();
System.out.println();
myGradeBook.displayMessage( nameOfCourse );

18. classes GradeBook and GradeBookTest are in the same default package
classes GradeBook and GradeBookTest are in the same default package. Classes in the same package are implicitly imported

19. Instance Variables
Variables declared in the body of a particular method are known as local variables and can be used only in that method
When that method terminates, the values of its local variables are lost
Attributes are represented as variables in a class declaration. Such variables are called fields (instance variables) and are declared inside a class declaration but outside the bodies of the class’s method declarations.
Each object (instance) of the class has a separate instance of the variable in memory

20. Variables or methods declared with access modifier private are accessible only to methods of the class in which they’re declared
Declaring instance variables with access modifier private is known as data hiding (encapsulation)
Unlike local variables, which are not automatically initialized, every field has a default initial value
The default value for a field of type String is null
variables of types byte, char, short, int, long, float and double are initialized to 0,
variables of type boolean are initialized to false

21. Programs use variables of reference types (normally called references) to store the locations of objects in the computer’s memory
Reference-type instance variables are initialized by default to the value null

22. Initializing Objects with Constructors

23. If..else

24. Nested if..else

25. Dangling-else Problem

26. Solve Dangling Problem

27. While loop

28. Increment and Decrement Operators

29. For Repetition

30. Application