Class & Object

By definition:

• A class is a blueprint—a template that defines the structure and behavior of objects.

• An object is a real-world instance of that class. It has its own state and behavior, as defined by the class.

To understand this intuitively, imagine a class as an application form template—like the one you'd fill when applying for a passport or a job.

🔹 Class = Form Template (Soft Copy)

This form contains:

• Blank fields like “Name”, “Age”, “Address” → These represent instance variables, which are filled per object.

• Predefined values like the issuing authority’s name or form version → These represent static constants or finalfields, already defined.

• Auto-generated fields like Date of Issue or Serial Number → These are like runtime-generated values, initialized through constructors or system code.

• Instructions or clauses → These are your methods, defining the behavior and rules of the form.

But this soft copy of the form can’t do anything on its own. It’s just a design—not usable until it's instantiated.

🔹 Object = Printed Form (Instance)

When you print the form, it becomes a usable copy. This is what we call the instantiation stage in the object lifecycle.

You’ve created the object, making it usable—but it’s still not yet ready, as the form is still blank.

At this stage, you can:

• Fill in the information (assign values to instance variables),

• Accept predefined values (static/final fields),

• Follow the instructions (execute methods).

Once you fill in the required details and invoke the relevant methods, the object transitions to an "In Use" state—it’s not just instantiated, it’s actively fulfilling its purpose.

🔻 Final Lifecycle Stage: Garbage Collection

Eventually, when the object (or this printed form) fulfills its purpose—for example, the form has been submitted, processed, and archived—it’s no longer needed.

At this point, the object enters the "Eligible for Garbage Collection" phase.

Just like a physical form that’s discarded after use, the object is removed from memory by the garbage collector in Java.