Declaration, Instantiation and Initialization are very confusing terms in Java. Let us clear their meanings with example :
Declaration
A variable is said to be declared when we give name to variable and associate it with a class.
Example :- Student stu; (here Student is a class)
Instantiation
Instantiation means we are creating an object or allocating memory. So use of new keyword to create an object and allocate memory is instantiation.
Initialization
Initialize means we are associating/assigning some values to an object. So to associate values with object we call constructor. So calling constructor is called initialization.
Example:- new Student(); (here we are instantiating object using new keyword and initializing object by calling constructor).