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  1. 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 1
  2. 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 2
  3. 3 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.
  4. 4 Objects are of same type SMARTPHONE S OBJECTS
  5. 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 5
  6. 6 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
  7. Creating an object smartphone samsung=new smartphone(); Each object has its own set of instance variable 7 samsung Refrence variable ManufracturerManufracturer ModelModel StorageStorage Screeen sizeScreeen size ManufracturerManufracturer ModelModel StorageStorage Screeen sizeScreeen size feilds OBJECT REFFERING TO
  8. Dot operator .  Object variables & methods can be accessed using the dot operator Example :- smartphone samsung = new smartphone(); samsung.model = galaxyprime; 8
  9. 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 } } 9
  10. 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; } } 10
  11. 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 11
  12. 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. 12
  13. 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; } } 13 Default values 0 0.0 null null false integer float character string boolean 0 10 0.0 20.0 m Null java False true
  14. 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 14
  15. 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 } } 15 OUTPUT volume of sphere 33.49 volume of cylinder 269.255
  16. 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 16
  17. 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}; 17
  18. 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 } } } 18
  19. 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] 19
  20. 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"); 20
  21. Java String Example 21 Output: java Strings example
  22. Some important operations of strings  String Concatenation  String Comparison  Substring  Length of String etc. 22
  23.  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 23
  24.  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 24
  25. 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 25
  26. 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. 26
  27. 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. 27
  28. Example of using StringBuffer & StringBuilder class 28  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() );
  29. Difference between String and StringBuffer 29
  30. 30 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
  31. 31 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”
  32. 32 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.
  33. 33 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 } }
  34. 34 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
  36. THANK YOU 36