Introduction to oop and java fundamentals

INTRODUCTION TO OOP AND
JAVA FUNDAMENTALS
N.ANSGAR MARY
AP/IT

Unit I
• Object Oriented Programming - Abstraction –
objects and classes - Encapsulation- Inheritance-
Polymorphism- OOP in Java – Characteristics of
Java – The Java Environment - Java Source File -
Structure Compilation. Fundamental
Programming Structures in Java – Defining classes
in Java – constructors, methods - access specifiers
- static members - Comments, Data Types,
Variables, Operators, Control Flow, Arrays,
Packages - JavaDoc comments.

OBJECT-ORIENTED PROGRAMMING
Object-Oriented Programming (OOP) is a programming
language model organized around objects rather than
actions and data. An object-oriented program can be
characterized as data controlling access to code. Concepts
of OOPS
• Object
• Class
• Inheritance
• Polymorphism
• Abstraction
• Encapsulation

OBJECT
• Object means a real word entity such as pen, chair, table etc.
• Any entity that has state and behavior is known as an object.
• Object can be defined as an instance of a class.
• An object contains an address and takes up some space in memory. Objects can
communicate without knowing details of each other's data or code, the only
necessary thing is that the type of message accepted and type of response
returned by the objects.
• An object has three characteristics:
• state: represents data (value) of an object.
• behavior: represents the behavior (functionality) of an object such as deposit,
withdraw etc.
• identity: Object identity is typically implemented via a unique ID. The value of the
ID is not visible to the external user. But, it is used internally by the JVM to identify
each object uniquely.

CLASS
• Collection of objects is called class.
• It is a logical entity.
• A class can also be defined as a blueprint from which
you can create an individual object.
• A class consists of Data members and methods.
• The primary purpose of a class is to hold
data/information.
• The member functions determine the behavior of the
class, i.e. provide a definition for supporting various
operations on data held in the form of an object.
• Class doesn’t store any space.

Example
public class Dog
{
String breed;
int age;
String color;
void barking()
{ }
void hungry()
{ }
void sleeping()
{ }
}

Constructors
• Each time a new object is created, at least one
constructor will be invoked. The main rule of
constructors is that they should have the same name
as the class. A class can have more than one
constructor.
Following is an example of a constructor −
Example
public class Puppy
{
public Puppy()
{ }
public Puppy(String name)
{ // This constructor has one parameter, name. } }

INHERITANCE
• Inheritance can be defined as the procedure or mechanism
of acquiring all the properties and behavior of one class to
another, i.e., acquiring the properties and behavior of child
class from the parent class.
• When one object acquires all the properties and
behaviours of another object, it is known as inheritance.
• It provides code reusability and establishes relationships
between different classes. A class which inherits the
properties is known as Child Class(sub-class or derived
class) whereas a class whose properties are inherited is
known as Parent class(super-class or base class).
• Types of inheritance in java: single, multilevel and
hierarchical inheritance. Multiple and hybrid inheritance is
supported through interface only.

POLYMORPHISM
• When one task is performed by different ways
i.e. known as polymorphism. For example: to
draw something e.g. shape or rectangle etc.

Polymorphism is classified into two ways:
Method Overloading(Compile time Polymorphism)
• Method Overloading is a feature that allows a class to
have two or more methods having the same name but
the arguments passed to the methods are different.
Compile time polymorphism refers to a process in
which a call to an overloaded method is resolved at
compile time rather than at run time.
Method Overriding(Run time Polymorphism)
• If subclass (child class) has the same method as
declared in the parent class, it is known as method
overriding in java. In other words, If subclass provides
the specific implementation of the method that has
been provided by one of its parent class, it is known as
method overriding.

ABSTRACTION
• Abstraction refers to the act of representing
essential features without including the
background details or explanations.
For example: phone call, we don't know the
internal processing. In java, we use abstract class
and interface to achieve abstraction.

ENCAPSULATION
• The wrapping up of data and methods into a single unit (called class) is known as
encapsulation.
• Data encapsulation is the most striking feature of a class. The data is not accessible
to' the outside world and only those methods, which are wrapped in the class, can
access it. These methods provide the interface between the object's data and the
program.
• i.e. mixed of several medicines. A java class is the example of encapsulation.
• This insulation of the data from direct access by 'the program is called data hiding.

Message Communication:
• 1. Creating classes that define objects and
their behaviour.
• 2. Creating objects from class definitions.
• 3. Establishing communication among objects.

Dynamic Binding
• Dynamic binding means that the code
associated with a given procedure call is not
known until the time of the call at runtime.

DIFFERENCE BETWEEN PROCEDURE-ORIENTED AND OBJECT-ORIENTED
PROGRAMMING

JAVA
• Java is a robust, general-purpose, high-level
programming language and a powerful software
platform. It is also object-oriented, distributed,
portable and multi-threaded. Java follows the 'Write -
once - run - anywhere' approach.
• All Java programs must run on the Java platform that
has two components,
i. Java Virtual Machine (JVM)
Ii.Java Application Programming Interface (API).
• With Java API, many types of Java programs can be
developed. These include
Java stand-alone applications
Java Applets
Java Servlets

Characteristics of Java language
• Compiled and Interpreted
• Platform-Independent and Portable
• Object-Oriented
• Robust and Secure
• Distributed
• Familiar, Simple. and Small
• Multithreaded and Interactive
• High Performance
• Dynamic and Extensible

THE JAVA PROGRAMMING
ENVIRONMENT:

STRUCTURE OF JAVA PROGRAM
A Java program involves the following sections:
• Documentation Section
• Package Statement
• Import Statements
• Interface Statement
• Class Definition
• Main Method Class
• Main Method Definition

COMPILATION AND EXECUTION OF A
JAVA PROGRAMCompilation
• First, the source .java‘ file is passed through the compiler, which
then encodes the source code into a machine independent
encoding, known as Bytecode. The content of each class contained
in the source file is stored in a separate .class‘ file.
Execution
• The class files generated by the compiler are independent of the
machine or the OS, which allows them to be run on any system. To
run, the main class file (the class that contains the method main) is
passed to the JVM, and then goes through three main stages before
the final machine code is executed. These stages are:
a. Class Loader
b.Bytecode Verifier
c.Just-In-Time Compiler

FUNDAMENTAL PROGRAMMING
STRUCTURES IN JAVA
• COMMENTS
– System.out.println("Hello, World!"); // comment
– /* and */
– /** to start and a */ to end
public class JavaApplication1
{
public static void main(String[] args)
{
System.out.println("welcome");
}
}

DATA TYPES
1) Integers
• Java defines four integer types: byte, short,
int, and long.

2. Floating-Point Types
3. Characters
It is a unification of dozens of character sets, such as Latin,
Greek, Arabic, Cyrillic, Hebrew, Katakana, Hangul, and many
more. For this purpose, it requires 16 bits. Thus, in Java char is
a 16-bit type. The range of a char is 0 to 65,536.
Although char is designed to hold Unicode characters, it can
also be thought of as an integer type on which you can
perform arithmetic operations
4. Booleans

Literals
• 1. Integer Literals
• 2. Floating-Point Literals
• 3. Boolean Literals
• 4. Character Literals
• 5. String Literals

VARIABLES• The variable is the basic unit of storage in a Java program.
• Declaring a Variable
type identifier [ = value][, identifier [= value] ...] ;
• int a, b, c; // declares three ints, a, b, and c.
• int d = 3, e, f = 5; // declares three more ints, initializing // d and f.
Dynamic Initialization:
double c = Math.sqrt(a * a + b * b);
The Scope and Lifetime of Variables
There are two general categories of scopes:
• global and
• local
Type Conversion and Casting -int value to a long variable
Casting Incompatible Types
int a;
byte b;
// ...
b = (byte) a;

OPERATORS
• 1. Arithmetic Operators:

• 4. Boolean Logical Operators
• 5. Short-Circuit Logical Operators

• 6. The Assignment Operator:
• 7. The ? Operator
– General form:
– expression1 ? expression2 : expression3

CONTROL STATEMENTS
Java‘s program control statements can be put
into the following categories:
• Selection statements
• Iteration statements
• Jump statements

1. Selection statements
Java supports two selection statements:
• if
• switch

2. Iteration Statements
Java‘s iteration statements are
• for
for(initialization; condition; iteration) {
// body
}
• do-while

• while
while(condition) {
// body of loop
}

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