Java class,object,method introduction

Pundra University of Science & Technology
Department of Computer Science & Engineering
Name: Md. Sihab Uddin
Batch No: 6th
Semester No: 4th
Roll No: 05

Outline
• Program Structure
• Concept of Class
• Concept of Object
• Concept of Constructor
• Method

Program Structure
• Structure
Import Statement
Package Statement
Class Definition
Inheritance Statement
Interface Statement
Main Method

Concept of Class
• A class is simply a representation of a type of object
• It is the blueprint/ plan/ template that describe the
details of an object
• For example- mango, apple, orange are the members of
the class fruits
• If fruits has been defined as a class, then the statement
Fruits mango;
• It will create an object mango belonging to the class
fruit

Cont……..
• Java is a case-sensitive language
• Class declaration
• Opening braces
• The main line
• The output line
Class Csepu
{
Public static void main (String args[])
{
System.out.println(“Java is better than C++”);
}
}

Cont……………
• Class declaration
Class Csepu
– This line uses the keyword class to declare that a new class is
being defined
– Csepu is the name of the class
• Opening braces
{
……
}
– The class definition begins with the opening curly brace ({) and
ends with the closing curly brace (}).
– The elements between the two braces are members of the class

Cont………..
• The main line
Public static void main (String args[])
– The keyword public means that the method main() can
be accessed by any other Java class.
– The keyword static means that you don’t have to create
an instance of this class to use this method.
– The keyword void means that the method main()
doesn’t return any value to the calling program.
– The keyword String[] args tells us that this method
will receive an array of characters as the argument

Cont…….
• The Output line
System.out.println(“Java is better than C++”);
– This is similar to the printf() statement of C
– Since Java is a true object oriented language, every method
must be part of an object
– The println method is a member of the out object, which is
a static data member of System class
– The method println always appends a newline character to
the end of the string
– This means that any subsequent output will start on a new
line

Object
• Objects are instances of a class. It is the building block
of OOP.
• They are the basic runtime entities in an object
oriented system
• They may present a person, a place, a bank account, a
table of data or any item that the program may handle
• Object must have the following three characteristics:
– Identity
– State
– Behavior

Concept of Constructors
• A constructor initializes an object when it is created
• It has the same name as its class and is syntactically similar to a method
• However, constructors have no explicit return type
• simple example class Adition
{ public void add()
{int a,b,add;
a=4;b=5;
add=a+b;
System.out.println("Result of Add:
"+add);
}
}
public class Exmcons1
{ public static void main (String args[])
{
Adition obj = new Adition();
obj.add();
}
}

Concept of Methods
• Methods are the interface or communications between
program components
• A Java method is a collection of statements that are grouped
together to perform an operation
• As an example when we call the System.out.println method…
– The system actually executes several statements in order to
display a message on the console
– In general, a method has the following syntax
Modifier returnValueType methodName (list of parameters)
{
//method of body;
}

Declaring a Methods
• Modifiers
– The modifier, which is optional, tells the compiler how
to call the method
– This defines the access type of the method
• Return Type
– A method may return a value
– The returnValueType is the data type of the value the
method returns
– Some methods perform the desired operations without
returning a value
– In this case, the returnValueType is the keyword void

Cont………….
• Method Name
– This is the actual name of the method
– The method name and the parameter list together constitute
the method signature
• Parameters
– A parameter is like a place holder
– When a method is invoked, pass a value to the parameter
– This value is referred to as actual parameter or argument
– The parameter list refers to the type, order, and number of
the parameters of a method
– Parameters are optional; that is, a method may contain no
parameters

Cont………….
• Method Body
– The method body contains a collection of statements that define
what the method does
• Example
– The following defined method called max()
– This method takes two parameters num1 and num2 and returns
the maximum between the two
public static int max(int num1, int num2)
{
int result;
if (num1 > num2)
result = num1;
else
result = num2;
return result;
}

Java class,object,method introduction

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