Object Oriented Programming unit 1 content for students

By
S.Asha
Assistant Professor
Dept of Information Technology
S.A.Engineering College
OBJECT ORIENTED PROGRAMMING

INTRODUCTION TO OOPAND JAVA
FUNDAMENTALS
Object Oriented Programming - Abstraction – objects
and classes – Encapsulation-Inheritance -
Polymorphism- OOP in Java – Characteristics of Java –
Fundamental Programming Structures in Java –
Defining classes in Java – constructors, methods -access
specifiers - static members -Comments, Data Types,
Variables, Operators, Control Flow, Arrays, Packages.

INTRODUCTION TO JAVA
JAVA was developed by James Gosling at Sun Microsystems
Inc in the year 1995, later acquired by Oracle Corporation.
It is a simple programming language.
Java makes writing, compiling, and debugging programming
easy.
It helps to create reusable code.
JAVA is a object-oriented programming language.
A general-purpose programming language made for
developers to write once run anywhere that is compiled Java
code can run on all platforms that support Java.

1.Object Oriented Programming: Java supports object oriented
programming concepts such as
Encapsulation
Abstraction
Inheritance
Polymorphism
2. Simple: Java is very easy to learn, and its syntax is simple and easy to
understand.
3.Secured: Java is secured because java programs run inside a virtual
machine sandbox. JVM consist of class loader and byte-code verifier.
4.Platform Independent: Java is a write once, run anywhere language.

5.Robust: Java is robust because:
It uses strong memory management.
Java provides automatic garbage collection for collecting the
unused objects.
There is a lack of pointers that avoids security problems.
6. Portable: Java is portable because
It provides the facility to execute the Java byte code in any OS
making it platform independent.
7. Architecture-neutral: Java is architecture neutral because there
is no implementation dependent features.

8. Dynamic: Java is a dynamic language because
It supports the dynamic loading of classes i.e classes are loaded on
demand.
9. Interpreted: Java is an interpreted programming language
because in high level programming languages like Java , the
programs are converted into byte codes when they are compiled.
At runtime java bytecode is interpreted(converted) into machine
code using java interpreter(part of JVM) in order to run the program.
10. High-performance: Since JAVA supports features like just-in-
time compiler, multithreading, garbage collection which increases
the performance of java.

 11. Distributed: Here the applications running on different
machines which are connected via internet/network can
interact/access the resources with each other using java's pre-
built libraries like RMI, EJB etc.

12. Multi-threaded: Java is a multithreaded programming
language because
In JAVA a single program can perform two or more than two
tasks simultaneously.

FUNDAMENTAL PROGRAMMING STRUCTURS IN JAVA

DEFINING CLASSES IN JAVA
A class is a user defined data type from which objects are
created.
It is a template or blueprint from which objects are created.
A class in Java can contain:
Fields
Methods
Constructors
Blocks

VARIABLES
 A variable is a container which stores the value while
the Java program is executed.
 Variable is a name of memory location.
 A variable is assigned with a data type.

TYPES OF VARIABLES
There are three types of variables supported in
JAVA.
1. Local Variable
2. Instance Variable
3. Static Variable

1) Local Variable
 A variable declared inside the body of the method is called
local variable.
2) Instance Variable:
 A variable declared inside the class but outside the body of
the method, is called an instance variable.
3) Static variable:
 A variable that is declared as static is called a static variable.
Memory allocation for static variables happens only once
when the class is loaded in the memory.

Data Type Default Value Default size
boolean false 1 bit
char 'u0000' 2 byte
byte 0 1 byte
short 0 2 byte
int 0 4 byte
long 0L 8 byte
float 0.0f 4 byte
double 0.0d 8 byte

COMMENTS
Comments are the statements in a program that are not
executed by the compiler and interpreter.
Advantages:
 Comments are used to make the program more readable by
adding the details of the code.
 It makes easy to maintain the code and to find the errors
easily.
 The comments can be used to provide information or
explanation about the variable, method, class, or any
statement.

TYPES OF JAVA COMMENTS
 There are three types of comments in Java.
 Single Line Comment
 Multi Line Comment
 Documentation Comment

PROGRAM
public class JavaPrograms
{
public static void main(String[] args)
{
int id=10;
System.out.println("id="+id);
}
}

Methods in JAVA:
 A method in Java is a collection of statements that
perform some specific task and return the result to
the caller.

ACCESS SPECIFIERS
The access modifiers in Java specify the accessibility
or scope of a field, method, constructor, or class.
 There are four types of Java access modifiers:
 Default
 Private
 Public
 Protected

Access
Modifier
within class within package outside
package by
subclass only
outside
package
Private Y N N N
Default Y Y N N
Protected Y Y Y N
Public Y Y Y Y

class Student
{
int id=1;
String name=“XXX”;
int age=15;
void display()
{
System.out.println(id+" "+name+" "+age);
}
public static void main(String args[])
{
}
}

OBJECTS
 It is a basic unit of Object-Oriented Programming and represents
real life entities.
An object consists of :
 State: It is represented by attributes of an object.
 Behavior: It is represented by methods of an object.
 Identity: It gives a unique name to an object and enables one
object to interact with other objects.
 Example of an object: dog

Syntax for creating an object:
classname objectname=new classname();
Example:
Student s=new Student();
Where
Student – class name
S-object name

class Student
{
int id=1;
String name=“XXX”;
int age=15;
void display()
{
System.out.println(id+" "+name+" "+age);
}
{
Student s = new student();
s.display();
}
}
Note: If we are using methods inside a class, then we must
create an object inside the main method()to invoke the method

CONSTRUCTORS
 It is a special type of method which is used to initialize an object.
 In Java, a constructor is a block of codes similar to the method.
 It is called when an instance of the class is created.
 At the time of calling constructor, memory for the object is
allocated
 Every time an object is created using the new () keyword, at least
one constructor is called.
 It calls a default constructor if there is no constructor available in
the class

RULES FOR CREATING JAVA CONSTRUCTOR:
There are two rules defined for the constructor.
 Constructor name must be the same as its class name
 A Constructor must have no explicit return type

TYPES OF JAVA CONSTRUCTORS
There are two types of constructors in Java:
 Default constructor (no-arg constructor)
 Parameterized constructor

STATIC MEMBERS
 The static keyword in Java is used mainly for memory
management.
 In Java, static members are those which belongs to the class and
we can access these members without instantiating the class.
 The static keyword can be used for variables, methods, blocks,
class etc.,

STATIC FIELDS
 We can create a static field by using the keyword static.
 The static fields can be accessed both by the static as well as
non-static methods.
 We can access static fields using the class name (without
creating an object).

STATIC METHODS
 We can create a static method by using the keyword static.
 Static methods can access only static fields.
 To access static methods there is no need to instantiate the
class, we can do it just using the class name.

STATIC BLOCKS
 These are a block of codes with a static keyword.
 In general, these are used to initialize the static members.
 JVM executes static blocks before the main method at the
time of class loading.

public class statmem_example {
static int data;
void display()
{
int data=15;
System.out.println("data="+data);
}
static void print()
{
System.out.println("The value of data="+data);
}

static
{
data=10;
System.out.println("The static method is invoked");
}
{
statmem_example ex=new statmem_example();
statmem_example.print();
ex.display();
}
}
}
}

OPERATORS
Operator is a symbol that is used to perform mathematical and logical operations.
For example: +, -, *, / etc.
There are many types of operators in Java which are given below:
 Unary Operator
 Binary operator
 Arithmetic Operator
 Shift Operator
 Relational Operator
 Bitwise Operator
 Logical Operator

Object Oriented Programming unit 1 content for students

Unary Operators:
 Operations are performed on single operands.
 They are used to increment, decrement or negate a value.

public class Unary_Example
{
{
int a=10;
System.out.println("Value of a=“+(-a));
System.out.println("Value of a=“+(a++));
System.out.println("Value of a="+(--a));
}
}

OUTPUT:
Value of a=-10
Value of a=10
Value of a=10

BINARY OPERATORS
 Operation is performed on two operands.
 Binary operators that are supported in JAVA are
 Arithmetic Operator
 Shift Operator
 Relational Operator
 Bitwise Operator
 Logical Operator

ARITHMETIC OPERATORS
 Addition
 Subtraction
 Multiplication
 Division
 Modulus
Example:
 int A=10,B=20;

RELATIONAL OPERATORS
 A relational operator checks the relationship
between two operands.
 If the relation is true, it returns 1;
 If the relation is false, it returns value 0.
 Relational operators are used in decision making
and loops.

RELATIONAL OPERATORS
 equal to
 not equal to
 greater than
 less than
 greater than or equal to
 less than or equal to
 instance of

PROGRAM
public class instanceof_example
{
public static void main(String args[]){
instanceof_example s=new instanceof_example();
System.out.println(s instanceof
instanceof_example);//true
}
}

BITWISE OPERATORS:
 Bitwise operator works on bits and performs bit-by-bit operation.
 Example:
 int a = 60, b = 13;
a b a&b a|b a^b ~a
0 0 0 0 0 1
0 1 0 1 1 1
1 0 0 1 1 0
1 1 1 1 0 0

LOGICAL OPERATORS
 Logical operators are used to check whether an
expression is true or false .
 They are used in decision making.
 The logical operators that are supported in JAVA are
 &&(logical and)
 || (logical or)
 ! (logical not)
 Example:
 A=true; B=false;

SHIFT OPERATORS
 The shift operator is a java operator that is used to
shift bit patterns right or left.
 There are two types of shift operators. They are
 Left shift(<<) and
 Right shift(>>)
 EXAMPLE: 8<<2=0
 8>>2=2

ASSIGNMENT OPERATOR
= (Simple assignment operator)
+= (Addition assignment operator)
-= (Subtraction assignment operator)
*= (Multiplication assignment operator)
/=(Division Assignment operator)
%=(Modulo division assignment operator)

public class AssignmentOp_Example {
{
int a= 20, b = 15;
System.out.println("a+=b="+(a+=b));
System.out.println("a-=b="+(a-=b));
System.out.println("a*=b="+(a*=b));
System.out.println("a/=b="+(a/=b));
System.out.println("a%=b="+(a%=b));
}
}

OUTPUT:
a+=b=35
a-=b=20
a*=b=300
a/=b=20
a%=b=5

TERNARY OPERATOR
Conditional Operator ( ? : )
SYNTAX:
variable x = (expression) ? value if true : value if false
Example:
int a=10,b=5;
b=a>b?a:b;

PRECEDENCE OF JAVA OPERATORS
Precedence operator tells us how an expression is evaluated.
Certain operators have higher precedence than others;
For example, the multiplication operator has higher precedence than
the addition operator.
 For example, consider the following expression,
 x = 10 + 5 * 2;
 So, the output is 20, not 30.
 Because operator * has higher precedence than +.

Category Operator Associativity
Postfix >() [] . (dot operator) Left to right
Unary >++ - - ! ~ Right to left
Multiplicative >* / Left to right
Additive >+ - Left to right
Shift >>> >>> << Left to right
Relational >> >= < <= Left to right
Equality >== != Left to right
Bitwise AND >& Left to right
Bitwise XOR >^ Left to right
Bitwise OR >| Left to right
Logical AND >&& Left to right
Logical OR >|| Left to right
Conditional ?: Right to left
Assignment >= += -= *= /= %= >>= <<=
&= ^= |=
Right to left

CONTROL FLOW
Java Control statements control the flow of execution based on data values and
conditional logic used in a program.
 There are three main categories of control flow statements;
 Selection statements: The selection statements checks the condition only once for the
program execution. Example: if, if-else and switch.
 Iteration statements: Iteration statements execute a block of code for several numbers
of times until the condition is true. Example: while, do-while and for.
 Transfer statements: Transfer statements are used to transfer the flow of execution
from one statement to another. break, continue, return.

SWITCH CASE STATEMENT
It is known as multi-way branching statement.
The switch statement begins with a keyword switch, followed by an
expression.
When the switch statement executes, it compares the value of the expression to
the values of each case label.
SYNTAX:
switch (<expression>)
{
case label 1: <statement1> case label 2: <statement2>
…
case label n: <statement>
default: <statement>
}

 Flow chart for Execution of FOR statements

TRANSFER STATEMENTS
 Transfer statements are used to transfer the flow of execution from
one statement to another.
Continue Statement:
 The continue statement in JAVA programming works somewhat like
the break statement. Instead of forcing termination, it forces the next
iteration of the loop to take place, skipping any code in between.
Break Statement:
 When a break statement is encountered inside a loop, the loop is
immediately terminated and the program control resumes at the next
statement following the loop.

public class ProgramContinue
{
{
System.out.println(“Odd Numbers”);
for (int i = 1; i <= 10; ++i)
{
if (i % 2 == 0)
continue;
System.out.println(i + “t”);
}
}
}

PROGRAM FOR BREAK STATEMENTS
public class ProgramBreak
{
{
System.out.println(“Numbers 1 - 10”);
for (int i = 1;; ++i)
{
if (i == 11)
break;
System.out.println(i + “t”);
}
}
}

OUTPUT:
Numbers 1 - 10
1
2
3
4
5
6
7
8
9
10

ARRAYS
 Array is a collection of elements of similar data types stored in
contiguous memory location.
 The array size is fixed.
 It is index based and the first element is stored at 0th
index.

Advantages of Array:
 Code Optimization
 Random access
Disadvantages of Array:
 Inefficient memory usage
Types of Array
There are two types of array.
 One Dimensional Array
 Multidimensional Array

One Dimensional Array: One-Dimensional Array is the
simplest form of an Array in which the elements are stored
linearly and can be accessed individually by specifying the index
value of each element stored in the array.
Syntax:
dataType[] arrayName=new datatype[size];
Or
dataType arrayName []=new datatype[size];
Example:
int[] a=new int[5];

DECLARING AN ARRAY
 Array can be created using the new keyword.
 To allocate memory for array elements we must
mention the array size.
 The size of an array must be specified by an int
value and not long or short.
 The default initial value of elements of an array is 0
for numeric types and false for boolean.

Syntax:
dataType arrayName[]=new datatype[size];
Or
dataType[] arrayName=new datatype[size];
Example:
int[] a=new int[5];
OR
int a[]=new int[5];

INITIALIZING AN ARRAY:
SYNTAX:
dataType[] arrayName=new datatype[]{list of values separated
by comma};
Example:
int[] a=new int[]{12,13,14};

import java.util.*;
public class Array_Example {
{
int number[]=new int[3];
System.out.println("Enter the array elements");
Scanner s=new Scanner(System.in);
number[0]=s.nextInt();
System.out.println("The numbers entered are"+number[0]+"
t"+number[1]+"t"+number[2]);
}
}

MULTIDIMENSIONALARRAYS:
 A multidimensional array is an array with more than two dimensions.
 In multi dimensional array the elements are stored in the form of
rows and columns.
 Syntax:
dataType[][] arrayName=new datatype[rowsize][columnnsize];
 Example:
int[][] a=new int[3][4];

JAGGED ARRAY
 Jagged array is an array of arrays with different row size i.e. with
different dimensions.
Example:
 int[][] a = {
{11, 3, 43},
{3, 5, 8, 1},
{9},
};

JAVA PACKAGE
 A java package is a group of similar types of classes,
interfaces and sub-packages.
 Package in java can be categorized in two form, built-
in package and user-defined package.
 There are many built-in packages such as java, lang,
awt, javax, swing, net, io, util, sql etc.
 Note: The package keyword is used to create a
package in java.

How to access package from another package?
There are two ways to access the package from outside the
package.
import package.*;
import package.classname;

PROGRAM:
package Package_Example;
public class Hello {
public String display()
{
return "Hello";
}
}

import java.util.*;
import Package_Example.*;
public class Package_Example {
{
System.out.println("Enter the student name");
Scanner in=new Scanner(System.in);
String name=in.next();
Hello h=new Hello();
System.out.println(h.display()+"t"+name);
}
}

OBJECT ORIENTED PROGRAMMING
 Definition: Object-oriented programming (OOPs) is a
methodology that simplifies software development and
maintenance by providing some rules.
 The main aim of OOP is to bind together the data and the functions
that operate on these data

OOPs Concepts:
 Class
 Objects
 Data Abstraction
 Encapsulation
 Inheritance
 Polymorphism
 Dynamic Binding
 Message Passing

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