What is the difference?

Question

A a;
A a=new A() ;

Answer 1

A a; - just declare object
A a = new A(); - declare and initialize object at the same time

Answer 2

A a; // you declare a variable a of type A with nothing in it
A a = new A() ; // you declare a variable of type A and initialize it with a new Object of type A.

a.dosomething() in the first case would throw a nullpointer exception and the second would execute the method dosomething

Answer 3

A a; declare object "null"
A a = new A(); declare and initialize object "allocated memory"

Answer 4

A a creates the variable new A(); creates the object