Becoz bean uses interospection to deside members of the class so it
need no argument constructor.

The no-args constructor allows tools or libraries to construct a bean of
a given class. There's not much point fiddling with the properties and
events of a bean if you can't construct it in the first place.

(Point of pedantry: "Default constructor" with this meaning is a C++
term. In Java a default constructor is just the synthetic constructor
provided by the compiler if no others are present.)

Tom Hawtin