Constructor in Java

Hello friends how are you, today in this blog i will teach you what is Constructor, types of Constructor , how Constructor works and many programs using Constructor  in a very simple way. 

Let's start

1.It is a special member function of class that executes when we create the instance(object) of that class.in other word we can say that there is no need to call a constructor.

2.Its name is same as class name.
3.It has no return type.
4.It may be parameterized or non-parameterized.
5.It is used to initialize class level variable.

Example

class Rectangle
{
//Data Member 
int height;
int width;
int area;
//constructor 
//notice here there is no return type and name is same as class name
Rectangle()
 {
  height=15;
  width=25;
  area=height*width;
  System.out.println("Area of Rectangle="+area);
 }
 public static void main(String[] args) 
 {
  //creating object
  //notice here no need to call a constructor
  Rectangle obj=new Rectangle();
 }
}
/*
### Output ###
Area of Rectangle=375
*/

Types of constructor

There are three types of constructor.

• Default Constructor.
• Parameterized Constructor.
• Copy Constructor.

Default Constructor

The constructor with no parameter is called default constructor.

class Rectangle
{
//Data Member 
int height;
int width;
int area;
//constructor 
//notice here there is no return type and name is same as class name
Rectangle()
 {
  height=15;
  width=25;
  area=height*width;
  System.out.println("Area of Rectangle="+area);
 }
 public static void main(String[] args) 
 {
  //creating object
  //notice here no need to call a constructor
  Rectangle obj=new Rectangle();
 }
}
/*
### Output ###
Area of Rectangle=375
*/

Parameterized Constructor

The constructor with parameter is called Parameterized constructor.

class Rectangle
{
//Data Member 
int area;
//constructor 
//notice here there is no return type and name is same as class name
Rectangle(int height,int width)
 {
  area=height*width;
  System.out.println("Area of Rectangle="+area);
 }
 public static void main(String[] args) 
 {
  //creating instance(object) of class
  /*notice here there are two value is passed
  because there are two parameter in constructor
  15 will assign to height and 25 will assign to width 
 */
  Rectangle obj=new Rectangle(15,25);
 }
}
/*
### Output ###
Area of Rectangle=375
*/

Copy Constructor

In this type of constructor one object with parameter is copied into another object so it is called copy constructor.

class Rectangle
{
//Data Member 
int area;
//constructor 
//notice here there is no return type and name is same as class name
Rectangle(int height,int width)
 {
  area=height*width;
 }
void show()
{
System.out.println("Area of Rectangle="+area);
}
 public static void main(String[] args) 
 {
  //creating instance(object) of class
  /*notice here there are two value is passed
  because there are two parameter in constructor
  15 will assign to height and 25 will assign to width 
 */
  Rectangle obj1=new Rectangle(15,25);
  obj1.show();
  //passing obj1 in obj2 
  Rectangle obj2=obj1;
  obj2.show();
 }
}
/*
### Output ###
Area of Rectangle=375
Area of Rectangle=375
*/

Destructor

1.There is no destructor in JAVA.

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