Java fundamentals

Java Fundamentals
Sohail Shaghasi
sohail.shaghasi@gmail.com

Course Overview
 What is computer program?
 What is high level and low level language?
 Introduction to Java.
 What is an IDE?
 How Java program Gets executed (Java life cycle)?
 What is Variable?
 What is Variable Scope?
 What is Constant?

Course Overview Cont.
 What is Operator?
 What is primitive type?
 What is String?
 What is array?
 What are control statements (if / else, Switch , For, while, Break/Continue)?
 What is function/Method?
 What is Class ?
 What is Constructor?
 What is Object ?
 What is Access Modifiers?
 What is OOP?
 Pillars of OOP

What is Computer Program?
 Program is a set of instruction given to a computer to perform a specific task.
 Some examples of computer programs:
 A web browser like Mozilla Firefox and Apple Safari can be used to view web pages
on the Internet.
 An office suite can be used to write documents or spreadsheets.
 Video games are computer programs.

What is High level and Low Level
language?
 Characteristics of High level languages:
 Easier to understand and user friendly.
 Extremely portable.
 Can be debugged in an easier manner.
 Characteristics of Low level language:
 Extremely difficult to understand.
 Nearer to Machine code.
 Appropriate for developing new operating system.
 Appropriate for microcontrollers programming.

Introduction to Java
 Programming language based on C and C++.
 Designed to be written once and run anywhere (cross platform).
 Runs on virtual machine.
 Very similar to C#.
 Java is Object Oriented.

What is an IDE?
 IDE means
 Integrated Development Environment.
 An IDE is software application.
 Eclipse, Netbeans and Microsoft Visual studio are IDEs.
 You can do many things using IDE
 Implement databases.
 Design User interfaces.
 Program an application.
 Compile/build an application
 Test an application.
 Debug an application.
 Diagraming.

Java life Cycle
 How Java program gets executed?

What is Variable?
 Just like a variable in a math equation
 1 + 3 = 4
 1 + x = ?
 Without variables programs would be non-interactive
 Variables allow us to store data in our program
 Opposite of a constant
 The number 3 is a constant
 X is a variable
Syntax:

What is Variable Scope?
 Global Variables:
 Declared outside any function.
 Local Variable:
 Declare inside a function.
 To simplify things, just think of the scope as anything
between the curly braces {…}. The outer curly braces are
called the outer blocks , and the inner curly braces are
called inner blocks.

What is constant?
 It is a variable whose value can’t change.

What is Operator?
 Assignment
 =
 +=
 -=
 *=
 /=
 %=

Operators Cont
 Relational
 >
 <
 >=
 <=
 ==
 !=

Operators Cont.
 Logical
 &&
 ||
 !

What is Array?
 An array is a group of contiguous or related data items that share a common name.
 Used when programs have to handle large amount of data
 Each value is stored at a specific position
 Position is called a index or superscript. Base index = 0
69
61
70
89
23
10
9
0
1
2
3
4
5
6
index
values

Array Cont.
 Like any other variables, arrays must declared and created before
they can be used. Creation of arrays involve three steps:
 Declare the array
 Create storage area in primary memory.
 Put values into the array (i.e., Memory location)
 String[] students = new String[10];
 String[] students = new String []{‘st1’, ‘st2’, ‘st3’};

What are Control statements?
 if else
 switch
 while
 do while
 For
 For Each
 break
 continue

If - else
if(conditional_statement)
{
statement to be executed if conditional_statement becomes true
}
Else
{
statements to be executed if the above conditional_statement
becomes false
}

Switch
switch (n)
{
case expression1:
// code to be executed if n is equal to expression1;
break;
case expression :
// code to be executed if n is equal to expression1;
break;
default:
// code to be executed if n doesn't match any expression1
}

Switch statement Flowchart

While loop
while(condition_statementtrue)
{
Statements to be executed when the condition becomes true and execute
them repeatedly until condition_statement becomes false.
}
E.g.
int x = 2;
while(x>5){
system.out.println(“value of x:”+x);
x++;
}

Do while loop
do
{
statements to be executed at least once without looking at the condition.
The statements will be executed until the condition becomes true.
}
while(condition_statement);

Comparing while and do-while loops

For loop
for(initialization; condition; increment/decrement){
statements to be executed until the condition becomes false
}
E.g:
for(int x = 0; x < 10; x++)
{
System.out.println(“value of x:”+x);
}

Break
 Break is used in the loops and when executed, the control of the execution will come out of the
loop.
E.g:
for(int i=1;i<50;i++)
{
if(i%11==0)
{
System.out.println(“Before breaking the loop”);
break;
}
System.out.println(“Value of i:”+i );
}

Continue
 Continue makes the loop to skip the current execution and continues with the next iteration.
E.g:
for(int i=1;i<50;i++)
{
if(i%11==0)
{
System.out.println(“Before breaking the loop”);
continue;
}
System.out.println(“Value of i:”+i );
}

What is function/Method?
 A function is section of a program that has a name and performs a specific
task.
 Function definition:
 Return Type − A function may return a value
 Function Name − This is the actual name of the function.
 Parameter List − A parameter is like a placeholder. When a function is
invoked, you pass a value as a parameter.
 Function Body − collection of statements that describes what the function
does.

Function Cont.
Access
Modifier
Return
type
Function
name
Method body
parameters
return

What is Class?
 Class can be thought of as a template, a prototype or a blueprint of an
object.
 It is a fundamental structure in Object oriented programming.
 Two types of class members:
 Fields (properties or attributes)
 Methods
 Specify the operations.

What is Constructor?
 Constructor is a method where you place all the initialization, it has the same
name as the class.
 When you create an object, you actually invoke the class constructor.
 “new” Operator
 Allocated a memory for that object and returns a reference of that memory
location to you.
 “Dot” operator
 It allows you to access public properties and public methods of a respective
class.

Constructor cont.

What is Object?
 An object is an instance of a class.
 To create an object the ‘new’ operator is used.
 For example if you want to create an instance of class String, we write the
following code,
 String str = new String(“Hello World”);
 Or also equivalent to
 String str = “Hello World”;

Object cont.
sohail.shaghasi@gmail.com Object

What are Access Modifiers?
Access
Modifier
within class within package outside
package by
subclass only
outside
package
Private Yes No No No
Default Yes Yes No No
Protected Yes Yes Yes No
Public Yes Yes Yes Yes

What is OOP?
 object-oriented programming:
 A programming paradigm where a software system is represented as a
collection of objects that interact with each other to solve the overall task.

Four Pillars of OOP
 Object-oriented programming is based on these 4 pillar:
 Abstraction
 Polymorphism
 Inheritance
 Encapsulation
APIE

Abstraction
 In java, we can have an abstract class without any abstract method. This
allow us to create classes that cannot be instantiated, but can only be
inherited.
 Abstract classes cannot be instantiated, means we cant create object to
Abstract class.
 We can create subclasses to Abstract classes.

Polymorphism
 Polymorphism is the capability of a method to do different things based on
the object.

Inheritance
 One of the most effective feature of OOP paradigm.
 Establish link/connectivity between 2 or more classes.
 Permits sharing and accessing properties from one to another class.
 To establish this relation java uses ‘extends’ keyword.

Encapsulation
 Encapsulation is the technique of making the fields in a class private and
providing access to the fields via public methods.
 If a field is declared private, it cannot be accessed by outside classes.
 Encapsulation is referred to as data hiding.

Java fundamentals

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Java fundamentals