1. Basics of Classes and Objects
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2. Objectives
On completion of this period, you would be able to
learn
• Class
• General form of class
• Object
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3. Recap
• In the previous class we learnt
• Language basics like
Selection statements
Iterative statements
Break and continue statements

4. Class Fundamentals
WWhat is an entity ?
• Anything that is uniquely identifiable
• It has attributes, which describe the entity
• If we provide methods to such entity
• We get a class
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5. Class Fundamentals …contd
Regarding the structure of a class
O How is ‘struct’ in C language designed ?
• It is a collection of heterogeneous types of data items
• A list variables are put together
• If we add methods (functions) to it, we get something
equivalent to a class
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6. Class Fundamentals contd
• Class
• Class is a template for an object
• It defines a new data type
• It contains data members and related methods
Examples of class
• Student
• Employee
• Rectangle
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7. General Form Of A Class
• While defining declare exact form and nature
• Specify the data and code that operates it
• Data declared in a class are called ‘instance variables’
• Simple class contains only code or only data
• Real world classes contain both code and data
• Class is declared by keyword ‘class’
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8. General Form Of Class contd..
User defined name
Syntax:
class classname {
type instance-variable1;
type instance-variable2;
--- ---
--- ---
type instance-variable N;
type methodname1(parameter-list) {
(body of method)
}
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9. General Form Of Class contd..
type methodname2(parameter-list) {
(body of method)
}
--- ---
--- ---
type methodnameN(parameter-list) {
(body of method)
}
}
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10. Discussion
• Compare the structure in C with class in Java
• Only data members are permitted in struct
• Data and methods are permitted in class
• Visibility control is not there in struct
• Visibility control is available
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11. Example
Class name – Box
Instance variables – width, height and depth
As class defines a type of data,
class Box { Here new data type is Box
double width;
double height;
double depth;
}
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12. Discussion
• List some more class examples with their data
and method members
• Product
– prodId, prodDesc, price, qty
– receive(), issue() [ in store environment]
• Bike
– model, regNo, color, cost, milage
– start(), stop(), accelerate(), applyBreak()
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13. Object – Definition
Object
• A software bundle of data and the related
methods
• Object is an instance of a class
• Object contains both state and behaviour
• State means its data members containing
specific values
• Behaviour means the collection of methods
defined in the object
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14. Object – Definition contd..
• Examples
• State
• A student with PIN 004-CM-601
• An employee with an id EMP608
• A rectangle with length 15 and width 8
• Behaviour
• setMarks(), getMarks(String PIN)
• computeSalary()
• computeArea(), setLength(),setWidth()
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15. Creating Object
Creating Object
• There are two steps to create an object
• Declare object
• Allocate memory and initialize the object
Syntax for declaring object
• ClassName objectName;
• eg. Box myBox;
Syntax for allocate memory and initialize
• objectName = new ClassName()
• eg. myBox = new Box();
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16. Creating Object contd..
Statement Effect
Box mybox null
mybox
mybox = new Box()
Width
mybox
Height
Depth
Box object
Fig. 14.1 Creating object
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17. Example On Classes And Objects
class Rectangle {
int length , width; //declaration of variables
void getData(int x, int y) //definition of method
{
length = x;
width = y;
}
int rectArea() //definition of another method
{
int area = length * width;
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18. Example On Classes And Objects contd..
return(area);
}
}
class Rectarea // class with main method
{
public static void main(String args[])
{
int area1,area2;
Rectangle rect1 = new Rectangle(); //creating objects
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19. Accessing Class Members
Rectangle rect2 = new Rectangle();
Rect1.length = 15; //Accessing variables
Rect1.width = 10;
Area1 = rect1.length * rect1.width;
rect2.getData(20,12); // Accessing methods
Area2 = rect2.rectArea();
System.out.println( “ Area1 =“ + area1);
System.out.println( “ Area2 =“ + area2);
}
}
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20. Output of Program
Area1 = 150 // Through Accessing variables
Area2 = 240 // Through accessing methods
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21. Summary
In this class we have discussed
• Class
• General form of a class
• Object
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22. Quiz
1. Among the following which is keyword to declare
a class ?
a) new
b) object
c) type
d) class
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23. Quiz Contd..
2 .To access member of a class which operator is
used ?
a) &
b) . (dot)
c) *
d) +
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24. Quiz Contd..
3. Object is
a) Inheritance of a class
b) Instance of a class
c) Subclass of a class
d) Super class of a class
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25. Frequently Asked Questions
1. What is a class ?
2. Mention the key word to declare a class
3. What are the common components of a class?
4. What is an object?
5. Write a program in Java for declaring a class and object
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java previous question papers
OCT/NOV-2012 QUESTION PAPER
April / May 2012 c-09
October/ November-2011 c-09
April/ May 2011 c-09
April/ May 2011 c-05
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