Core Java - Fundamentals III (Types of Variables)

• Variables are of two types primitive (eg: int) and reference (objects).
• Variables are also divided into 3 types, instance, static and local variables

    Instance Variables (Object Level Variables / Attributes)

• Varies from object to object.
• Scope is the same as object.
• Can be declared in class, constructor or outside of any method or block.
• Cannot be accessed from static area directly but we can access using object reference.
• Can be accessed in instance area directly.
• JVM provides default values, not required to initialize explicitly.

   Static Variables (Class Level Variables / Fields)

• Doesn't vary from object to object, need to declare at class level using static modifier.
• Single copy accessible across all objects. Scope is same as that of class.
• Available during class loading and destroyed during unloading.
• Static method is recommended to be called by class name instead of object reference.
• JVM provides default values, not required to initialize explicitly.
• Changes in values are reflected across all objects.

   Local Variables (Stack variables, Automatic/Temporary Variables)

• Inside a block or method, destroyed once method or block is completed.
• Need to perform initialization explicitly, else we get C.E.
• Only Applicable modifier is final.