Constructor

Constructor:

A constructor is a function which would be executed only at the time of creating an object.

      When the object is created the constructor will be executed.

Example:

Class A

{

int   i,j;

A ()

{

System.out.println (“inside constructor A()”);

I=5;

J=6;

}

Void fun ()

{

system.out.println (“i”);

system.out.println (“j”);

}

Public static void main (String args[])

{

A a=new A();

a.fun ();

}

}

Comparisons between a constructor and a function:

·        A normal function can be called as and when we required to call it, but we can’t call a constructor as and when we want.

·        Constructor would be executed only once on the object and that too, only at a time of object creation. A function can be called on an object as many number of times as we want.

·        Name of the function can be any name, but name of the constructor must and should be the name of the class.

·        A constructor will not have any return type, where as a function should have a return data type (at least void).

·        The keyword static can’t be used with constructors. It is applicable to functions and other variables.

·         We know that whenever jvm encounters the new operator, it creates an object of that class and loads the non-static members of the class into that object and then the address of object is assigned to a variable.

            But something other than this happens prior to this when JVM encounters the new operator, here we can see the function of constructors.

There are three types of constructors

1. Parameterized constructor

2. Copy constructor

3. Dafault constructor

Normally copy constructor does not used in java.

Parameterized constructor: the constructor which have the arguments, that in any number of arguments.

Example:

Class X

{

Int a, b;

          X(int i)

          {

A=I;

s.o.p(“inside constructor”);

}

X(int i, int j)

{

a=I;

b=j;

s.o.p(“inside constructor”);

}

Public static void main(String args[])

{

X  x= new X(6);

X x = new X(7,9);

}

}

Default constructor: the constructor which doesn’t have the arguments is known as default constructor.

Example:

    A(){}

If you don’t declare any constructor in a program it will take default constructor. We can’t see the constructor the compile will automatically execute that statement. In every constructor the first statement is super.