Constructor in java

Presented by,
Siva Shankari Rajan,
CPSV

CONTENTS
What is Constructor
Types of Constructor
Constructor overloading
1
2
3
4
Passing initial values as
arguments

1
Java Constructor
A constructor in Java is a
special method that is used
to initialize objects. The
constructor is called when an
object of a class is created. It
can be used to set initial
values for object attributes

2
Rules for Java Constructor
The constructor
name must match
the name of the
class
The default
constructor is
ALWAYS as no-arg
constructor
Constructors can
use any access
modifier, including
private
Constructors
must not have a
return type.

3
Difference Between Constructor and Method
Constructor are
used to initialize
the state of
object
Constructor
must not have
return type
Constructor
compil er provide
default
constructor .
Method is expose
the behaviour of
object.
Method must have
return type.
Method compiler
does't provide.
1
2
3
1
2
3

4
Types of Java Constructor
Default
constructor
Parameterized
constructor
Copy
constructor

5
01
02
A constructor that
have no parameter is
known as default
constructor.
Syntax of default
constructor:
<class_name>(){}
Default Constructor
Class Measuring
{
Private double Metre;
Private double kilometer;
Private double centimeter;
Private double Millimeter;
Measuring()
{
Metre=120; kilometer=10.0; centimeter=12.0;
Millimeter=5.0;
}
Void display()
{
System.out.println(“kilometer=“+kilometer);
}
}
Output:
Kilometer=10.0

6
01
02
A constructor that have
parameters is known as
parameterized
constructor.
Parameterized
constructor is used to
provide different values to
the distinct objects
Parameterize
dconstructor
Class Rectangle
{
int length; int breadth;
Rectangle(int len, int bre)
{
length=len;
breadth=bre;
}
}
Class demo
{
Public static void main(String args[])
{
Rectangle r1= new Rectangle(20,10);
System.out.println(“length of rectangle=“
r1.length);
System.out.println(“breadth of
rectangle=“ r1.breadth);
}}

7
01
02
We can create the object
with any initial value to
extract values in the
parameterized
constructor
Parameterized
constructor can pass a
value as:
1. An implicit call
2. An explicit call
Passing initial values
As arguments
Implicit call constructor:
It retrieves the parameterized
constructor even if it is not declared in
the main().
We can create the object with any
initial value to extract values in the
parameterized constructor
Explicit call constructor:
It helps in creating a temporary
instance.
A temporary instance remains in the
memory as long as it is being used in an
expression.

8
01
02
It is used to create a
temporary object of a
class object.
A copy constructor takes
only one argument, which
is of the type as the class.
Copy
constructor
Class Rectangle
{
int length; int breadth;
Rectangle(int len, int bre)
{
length=len;
breadth=bre;
}
Rectangle(Rectangle obj)
{
System.out.println(“copy constructor
invoked”);
length=obj.len;
breadth=obj.bre;
}
int area()
{
return(length*breadth);
}

9
01
02
It is used to create a
temporary object of a
class object.
A copy constructor takes
only one argument, which
is of the type as the class.
Copy
constructor
Class demo
{
{
Rectangle r1= new Rectangle(20,10);
Rectangle r2=new Rectangle(r1);
System.out.println(“area of 1st rectangle=“
r1.area());
System.out.println(“area of 2nd rectangle=“
r2.area());
}}

10
01
02
A constructor may be
overloaded, so a single
class may have more
than one constructor, all
of which have the same
name but different
argument lists.
Constructor
overloading
Class overloading
{
int x,
float y;
Overloading()
{x=0;y=0.0;}
Overloading(int a)
{x=a; y=0;}
Overloading(int a, float b)
{x=a; y=b;}
{
Overloading ov1=new overloading();
Overloading ov2=new overloading(40);
Overloading ov3=new overloading(10,4.5);
}
}

Constructor in java

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