constructor
- Constructor is used to initialize the instance variables
- At the time of object creation if corresponding constructor exists for that object in class then it will execute automatically.
Rules for constructor
- Constructor name and class name must be same
- Constructor does not return any value even void also
Types of constructor : 2 Types
- Default constructor
- parameterized constructor
Default constructor :
- A constructor which has no parameter is called default constructor
Syntax
class classname
{
classname()
{
body of default constructor;
}
}
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Program : Defualt constructor program
Program name : DefConDemo1.java
Output :
Default constructor
class DefConDemo1
{
DefConDemo1()
{
System.out.println("Default constructor");
}
DefConDemo1()
{
System.out.println("Default constructor");
}
public static void main(String args[])
{
DefConDemo1 d = new DefConDemo1();
}
}
Compile : javac DefConDemo1.java
Run : java DefConDemo1
Output :
Default constructor
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Note
- If class have no default constructor then compiler will create the default constructor automatically.
- Default constructor will provide the defalut values to object.
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Program : Defualt constructor program
Program name : Company.java
Output :
Id is : 0
Name is : null
class Company
{
int id ;
String name ;
Company()
{
System.out.println("Id is :"+id);
System.out.println("Name is :"+name);
}
public static void main(String args[])
{
Company c = new Company ();
}
}
Compile : javac Company.java
Run : java Company
Output :
Id is : 0
Name is : null
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Parameterized constructor
- A constructor that has parameter is known as parameterized constructor.
Why parameterized constructor?
- Parameterized constructor is used to provide different values to the distinctobjects.
Syntax
class classname
{
classname(list of parameters)
{
body of parameterized constructor;
}
}
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Program : Parameterized constructor program
Program name : Student.java
Output :
Id is : 1
Name is : Mohan
Id is : 2
Name = Nireekshan
class Student
{
int id ;
String name ;
Student(int i, String n)
{
id =i;
name = n;
System.out.println("Id is :"+id);
System.out.println("Name is :"+name);
}
public static void main(String args[])
{
Student s1 = new Student(1, “Mohan”);
Student s2 = new Student(2, “Nireekshan”);
}
}
Compile : javac Student.java
Run : java Student
Output :
Id is : 1
Name is : Mohan
Id is : 2
Name = Nireekshan
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Thanks for your time.
Thanks for your time.
Nireekshan