Java Constructor

what is constructor?

A constructor is special method used to initialize objects.

• The constructor is called when an object of a class created.
• constructor is name must match the class name.
• it cannot have a return type(like void).
• constructors can not inherited by subclass, but the constructor of the superclass can be invoked from the subclass. 
• All classes have constructors by default: if you do not create a class constructor yourself, Java creates one for you. 
• Constructors are called only once at the time of Object creation while method(s) can be called any number of times. 
• Constructor in Java can not be abstract, final, static, or Synchronized.

Types of constructors in Java 
Default constructor 
Parameterised Constructor 
Copy constructor

 ➤Default constructor 

• A constructor that has no parameters is known as default the constructor. 
• if we create a default constructor with no arguments, the compiler does not create a default constructor

➤Parameterised constructor 

• A constructor that has parameters is known as parameterized constructor. 

 1) Example of parameterised constructor 

 public class A

 {

 int x; 

 public A(int y)

 {

 x = y;

 }

 public static void main(String[] args) 

{ 

A obj = new A(5);

 System.out.println(obj.x);

 }

 } 

 2)Example of parameterised constructor (using "this" keyword)

 public class A 

{ 

 int x; 

 public A(int x) 

{ this.x=x; 

 }

 //constructor 

 public static void main(String[] args) 

{

 A obj = new A(5);

 System.out.println(obj.x);

 }

 }

 ➤Copy constructor 

•  Like C++, Java also supports a copy constructor. But, unlike C++, Java doesn’t create a default copy constructor if you don’t write your own.

NOTE : 

•  If constructors are inherited (class is inheriting other classes) then always first parent class's constructors invoke first one by one then child classes. 
• Java does not call a parameterized constructor implicitly, you need to explicitly invoke parameterised constructor.
• In Java, when you create an object of a child class, the default constructor of the parent class is implicitly called. If the parent class has a parameterized constructor and no default constructor is explicitly defined, you need to ensure that the child class constructor explicitly calls the appropriate parent constructor using the super keyword