Core Java Complete Notes By Durga Sir

Durga Sir’s Core Java Notes are widely recognized as a "goldmine" for both beginners and experienced developers, particularly for those preparing for SCJP/OCJP certification exams. These materials from

1. Definition Executing multiple threads simultaneously. core java complete notes by durga sir

D. Abstraction

• Abstract Class: Partial implementation. Cannot instantiate. Can have concrete methods.
• Interface: Full contract (100% abstraction before Java 8). After Java 8, default and static methods allowed. After Java 9, private methods allowed.

• Overloading (Compile-time): Automatic promotion in overloading (byte → short → int → ...). Why changing return type alone isn't overloading.
• Overriding (Runtime): Covariant return types (Java 5 onward). The rule: Parent’s method throws a checked exception → Child must throw the same or its subtype, or none.