Constructor in java is a special type of method that is used to initialize the object.
Java constructor is invoked at
the time of object creation. It constructs the
values i.e.
provides data for the object that
is why it is known as constructor.
Rules
for creating java constructor
There are basically two rules
defined for the constructor.
1.
Constructor name must be
same as its class name
2.
Constructor must have no
explicit return type
3.
A
Java constructor cannot be abstract, static, final, and synchronized
Types of
java constructors
There are two types of
constructors:
1.
Default constructor
(no-arg constructor)
2.
Parameterized
constructor
Java
Default Constructor
|
A constructor that
have no parameter is known as default constructor.
|
Syntax
of default constructor:
1.
Accessmodifier <class_name>(){l+s}
NOTE: If there is no
constructor in a class, compiler automatically creates a default
constructor.
|
If a class has default constructor, while creating
object for the class no need to
provide any parameter values.
|
|
Classname refvar=new
classname();
|
Q) What
is the purpose of default constructor?
Default constructor provides the
default values to the object like 0, null etc. depending on
the type.
Java
parameterized constructor
|
A constructor that
have parameters is known as parameterized constructor.
2.
Accessmodifier <class_name>(datatype p1,datatype
p2,…){l+s}
|
Why
use parameterized constructor?
|
Parameterized
constructor is used to provide different values to the distinct objects
|
|
If a class has parameterized constructor, while
creating object for the class need to provide
parameter
values.
|
|
Classname refvar=new
classname(p1value,p2value,p3 value);
|
Constructor
Overloading in Java
|
Constructor
overloading is a technique in Java in which a class can have any
number of constructors that differ in parameter lists
and datatype.The compiler differentiates
these constructors by taking into account
the number of parameters in the list and their
type.
|
Difference
between constructor and method in java
There are many differences
between constructors and methods. They are given below.
|
Java
Constructor
|
Java
Method
|
|
Constructor is used to
initialize the state of an object.
|
Method is used to
expose behaviour of an object.
|
|
Constructor must not
have return type.
|
Method must have
return type.
|
|
Constructor is invoked
implicitly.
|
Method is invoked
explicitly.
|
|
The java compiler
provides a default constructor if you don't have any constructor.
|
Method is not provided
by compiler in any case.
|
|
Constructor name must
be same as the class name.
|
Method name may or may
not be same as class name.
|
Quiz On Constructor:
1)public class Test{
void Test{
System.out.println("Like ThisVideo");
}
public static void main(String[] args){
new Test();
}
}
1)Like ThisVideo
1)Like ThisVideo
ii)No Output
iii)Exception will be thrown
iv)compilation issue
2)
