CLASSES, OBJECTS, METHODS,
CONSTRUCTORS, ARRAY, STRING & VECTOR
Presented By: SHIVAM
Reg Id:11701112
MCA 2nd
Semester
Department of Computer Science and Applications
D.A.V. University , Jalandhar
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CONTENTS
1. Introduction to objects
2. Introduction to classes
2.1 Instance of a class
1. Creating objects
3.1 Dot operator
1. Methods
4.1 Method overloading
1. Constructors
5.1 Constructor overloading
1. Array
6.1 Declaration, Initialization &allocation of array
6.2 Two dimentional array
1. Strings
7.1 operations of strings
7.2 String buffer classes
1. vectors
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Introduction
 Java is a true OO language and therefore the
underlying structure of all Java programs is classes.
 Anything we wish to represent in Java must be
encapsulated in a class that defines the “state” and
“behaviour” of the basic program components known as
objects.
 Classes create objects and objects use methods to
communicate between them. They provide a
convenient method for packaging a group of logically
related data items and functions that work on them.
 A class essentially serves as a template for an object
and behaves like a basic data type “int”. It is therefore
important to understand how the fields and methods are
defined in a class and how they are used to build a
Java program that incorporates the basic OO concepts
such as encapsulation, inheritance, and polymorphism.

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Objects are of same type
SMARTPHONE
S
OBJECTS

Classes
 Defines a new DATA TYPE.
 This new type can be used to create
objects of that type.
 So a class is a template for an object and
an object is an instance of a class
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Instance of Classes
 A class provide a blueprint from which individual
objects are created.
 Each object has some components which categorizes it
into a class.
Example:-
class smartphone
{
String manufacturer;
String model;
Double storage;
Double screensize;
}
Feilds
}
Only template is created. Now we can have different types of smartphones

Creating an object
smartphone samsung=new smartphone();
Each object has its own set of instance variable
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samsung
Refrence
variable
ManufracturerManufracturer
ModelModel
StorageStorage
Screeen sizeScreeen size
ManufracturerManufracturer
ModelModel
StorageStorage
Screeen sizeScreeen size
feilds
OBJECT REFFERING TO

Dot operator .
 Object variables & methods can be
accessed using the dot operator
Example :-
smartphone samsung = new smartphone();
samsung.model = galaxyprime;
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Methods
 Classes need to contain data and behaviour.
 Methods represent the behaviour of a class.
Example :-
class smartphone
{
double storage; // Feild
Void clickpicture() // Adding method to class smartphone
{
storage = storage-2; // behaviour or interaction
}
}
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Method Overloading
 Methods of same name but different signatures
Example
class smartphone{
int Storage=1000;
int astorage(int ram) // Method 1
{
int WithRAM=storage+ram;
return withRAM ;
}
int astorage(int ram, int sd) // Method 2
{
int withSD=storage+ram+sd
return withSD;
}
}
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Example cntd.
Class methodoverloading
{
public static void main(string args[])
{
Overloading total=new overloading();
int withRam=total.astorage(512); // invokes method 1
int withSD=total.astorage(512,1024); // invokes method 2
System.out.println(“Storage With RAM ”+withRAM);
System.out.println(“Storage with SD ”+withSD);
}
}
Output
Storage with RAM 1512
Storage with SD 2536
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Constructor in Java
 Constructor is a special method which will be
called automatically when we create an object
of any class.
 The main purpose of using constructor is to
initialize an object.
Properties of constructor:-
 Constructor name must be same as class name
 Constructor will be called automatically
 Constructor can’t return any value even void.
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Constructor eliminate default values
Class A
{
int a;
float b;
char ch;
string str;
boolean bl;
a()
{
a=10;
b=20.0;
ch=’m’;
str=“java”;
bl=true;
}
}
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Default values
0
0.0
null
null
false
integer
float
character
string
boolean
0 10
0.0 20.0
m
Null java
False true

CONSTRUCTOR OVERLOADING
 Constructor overloading in java allow us to have more
than one constructor in one class
 Similar to Method overloading, in constructor
overloading we have multiple constructor with different
signature the only difference is constructor doesn’t have
a return type
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Example
class volume
{
double pi=3.14;
volume(double radius) // Constructor 1
{
double sphere=4.0/3*pi*radius*radius*radius;
System.out.println(“volume of sphere”=+sphere);
}
volume(double radius,double height) // Constructor 2
{
double cylinder=pi*radius*radius*height;
System.out.println(“volume of cylinder”=+cylinder);
}
}
Class multipleconstructor // Main classs
{
public static void main(String args[])
{
volume sphere=new volume(2.0); // Invokes constructor 1
volume cylinder=new volume(3.5,7.0); // Invokes constructor 2
}
}
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OUTPUT
volume of sphere 33.49
volume of cylinder 269.255

Array
 An array is a container object .That holds a fixed number of values
of a single type.
 Each item in an array is called an element
 Element can be accessed through index number
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Array Declaration,Allocation & Initialization
 Array Declaration
Datatype arrayname[];
int[] arr; //int is a data type of array “arr” is the name of Array “[]” is for index.
 Array Allocation means size of array
Array can be allocated as:
int arr[]=new int[10];
New allocate memory for Array
 Array Initialization
• Array can be initialized by individual index
•arr[0]=1;
•arr[1]=2;
• Array can be declare , allocate and initialize in single statement as
•Int arr[ ]={1,2,3,4,5,6,7,9,10};
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Two Dimensional Array in java
 Declaration of Two dimentional Array
int[][] arr=new int[3][3]; //3 row and 3 column
 Example
class Testarray
{
public static void main(String args[])
{
int arr[][]={{1,2,3},{2,4,5},{4,4,5}}; //declaring and initializing array
for(int i=0;i<3;i++) //printing array
{
for(int j=0;j<3;j++)
{
System.out.print(“”+arr[i][j]);
}
System.out.println(); // After displaying one row move cursor to next line
}
}
}
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Arr[i][j] Column 1 [0] Column 2 [1] Column 3 [2]
Row 1 [0] 1
Arr[0][0]
2
Arr[0][1]
3
Arr[0][2]
Row 2 [1] 2
Arr[1][0]
4
Arr[1][1]
5
Arr[1][2]
Row 3 [2] 4
Arr[2][0]
4
Arr[2][1]
5
Arr[2][2]
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Strings
 A sequence of characters
 Java platform provides the String class to create
and manipulate strings.
 How to create String object?
There are two ways to create String object:
 By string literal
For Example:
String s="welcome";
 By new keyword
For Example:
String s=new String("Welcome");
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Java String Example
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Output:
java
Strings
example

Some important operations of strings
 String Concatenation
 String Comparison
 Substring
 Length of String etc.
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 Concatenating String()
Concatenate two or more string.
string str = “mca";
string str1 = “class";
string str2 = str + str1;
string st = “mca"+“class";
 String Comparison()
It compares the content of the strings. It will return true if string
matches, else returns false.
String s1 = "Java";
String s2 = "Java";
String s3 = new string (“ABC");
test(s1 == s2) //true
test(s1 == s3) //false
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 substring()
substring() method returns a part of the string.
String str = "0123456789";
System.out.println(str.substring(4));
Output:
456789
System.out.println(str.substring(4,7));
Output:
456
 length()
length() function returns the number of characters in a String.
String str = "Count me";
System.out.println(str.length());
Output:
8
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Some more string class methods
 The java.lang.String class provides a lot of methods to work on string. By the help
of these methods, we can perform operations on strings.
 Here are some other methods :
1. charAt() :-returns a char value at the given index number. The index number
starts from 0.
2. contains():- . It returns true if sequence of char values are found in this string
otherwise returns false.
3. getChars() :-copies the content of this string into specified char array
4. indexOf() :-returns index of given character value or substring.
5. replace() :-returns a string replacing all the old char or CharSequence to new char
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StringBuffer class
 Java StringBuffer class is used to created mutable (modifiable) string.
 Important Constructors of StringBuffer class:
1. StringBuffer(): creates an empty string buffer with the initial capacity of 16.
2. StringBuffer(String str): creates a string buffer with the specified string.
3. StringBuffer(int capacity): creates an empty string buffer with the specified
capacity as length.
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Important methods of StringBuffer class
append(String s): is used to append the specified string with this string.
insert(int offset, String s): is used to insert the specified string with this
string at the specified position.
replace(int startIndex, int endIndex, String str): is used to replace the
string from specified startIndex and endIndex.
delete(int startIndex, int endIndex): is used to delete the string from
specified startIndex and endIndex.
reverse(): is used to reverse the string.
capacity(): is used to return the current capacity.
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Example of using StringBuffer & StringBuilder class
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 Append()
StringBuffer str = new StringBuffer("test");
str.append(123);
System.out.println(str);
 insert()
StringBuffer str = new StringBuffer("test");
str.insert(4, 123);
System.out.println(str);
 replace()
StringBuffer str = new StringBuffer("Hello World");
str.replace( 6, 11, "java");
System.out.println(str);
 capacity()
StringBuffer str = new StringBuffer();
System.out.println( str.capacity() );

Difference between String and StringBuffer
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Vector
 The Vector class implements a growable array of
objects.
 Like an array, accessed using an integer index.
 Vector can grow or shrink as needed to accommodate
adding and removing items.
 In Java this is supported by Vector class contained in
java.util package. Can hold objects of any type or any
number. The objects do not have to be homogeneous.
 Like arrays, Vectors are created as follows:
 Vector list = new Vector(); // declaring without size
 Vector list = new Vector(3); // declaring with size

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Vector properties
 Vectors posses a number of advantages over
arrays:
 It is convenient to use vectors to store objects.
 A vector can be used to store list of objects that may
vary in size.
 We can add and delete objects from the list as an
when required.
 But vectors cannot be used to store basic data
types (int, float, etc.); we can only store objects.
To store basic data type items, we need
convert them to objects using “wrapper classes”

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Important Methods in Vector class
 addElement(Object item)
 insertElementAt(Object item, int index)
 elementAt(int index) – get element at index
 removeElementAt(int index)
 size()
 clone() - Returns a clone of this vector.
 clear() - Removes all of the elements from this Vector.
 get(int index) - Returns the element at the specified
position in this Vector.
 copyInto(array) – copy all items from vector to array.

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Vector – Example
import java.util.*;
public class VectorOne{
public static void main(String[] args) {
Vector circleVector = new Vector();
System.out.println("Vector Length = “ +circleVector.size()); // 0
for ( int i=0; i < 5; i++) {
circleVector.addElement( new Circle(i) );
// radius of the Circles 0,1,2,3,4
}
System.out.println("Vector Length = " + circleVector.size());// 5
}
}

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Summary
 Classes, objects, and methods are the basic
components used in Java programming.
 We have discussed:
 How to define a class
 How to create objects
 How to add methods to classes
 How to add constructor
 Array , string, and vector

REFERENCES
RAJAN MANRO & SUNITA M. 2014
JAVA & WEB DESIGNING KALYANI PUBLISHERS
ABHIJEET SINGH. 2016 CONCEPT OF STRING AND SRING BUFFER
www.studytonight.com
Sonoo Jaiswal 2015 Array and vector
www.javatpoint.com
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THANK YOU
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