Constructors

A constructor initializes an object instantly upon creation. It has the similar name as the class in that it resides and is syntactically same to a method. At one time defined, the constructor is automatically known as instantly after the object is created, before the new operator completes. A Constructor looks a little strange since they have no return type and not even void. This is why the implicit return type of a class' constructor is the class type itself. That is the constructors' job to initialize the internal state of an object so in which the code creating an example will have a fully initialized, usable object instantly.

Before moving on, let's reexamine a new operator.  As you know, whenever you allocate an object, you use the following common form:

Class-var = new classname();

Now you can understand why the parentheses are required after the class name. What is in fact happening is which the constructor for the class is being called therefore, in the line

Box mybox1= new Box();

New Box () is calling the Box () constructor. Whenever you do not explicitly describes a constructor for a class, and then Java creates a default constructor for the class. This is because the preceding line of code worked in previous versions of box which did not define a constructor.