Do you mean declaration and instantiation? You can declare a variable at any time, but the object is not created until it is instantiated. A variable can be declared for a File object, but the file object does not exist as it has not been instantiated (or created):
The File object can then be instantiated (created) with this line:
Dear Readers, I hope that what I say is clear because if it is not clear then please forgive me for my poor teaching skills. BUT if you find it useful then at least reply back saying that it was useful.
Ok, let's say you want an apple and you say that "I want an apple!". This is similar to saying that you want a variable and therefore declare it. BUT Remember that by just saying you want an apple you won't get it. Similarly, no memory space will be reserved for that variable by just simply declaring it. You will have to go and buy the apple which is similar to instantiating a variable by giving it some value (like you give money for that apple).
I just tried explaining it in a different style. Please forgive me if you got more confused by reading this.
A method declaration just says that there is a method with a specific signatures. A methode definition defines what that method does.
An interface, for example, only contains method *declarations*. A method *definition* is the methods code.
At least that's my understanding...
The soul is dyed the color of its thoughts. Think only on those things that are in line with your principles and can bear the light of day. The content of your character is your choice. Day by day, what you do is who you become. Your integrity is your destiny - it is the light that guides your way. - Heraclitus