Java OOP Concepts - Exam Revision
1. Inheritance (IS-A Relationship)
Allows a child class (subclass) to inherit properties (fields/methods) from a parent class
(superclass).
- Keyword: extends
- Advantage: CR (Code Reusability)
- Disadvantage: TC (Tightly Coupled Classes)
- Types:
- Single Inheritance (One parent -> One child)
- Multilevel Inheritance (Parent -> Child -> Grandchild)
Example:
class Parent {
void show() { System.out.println("Parent class method"); }
}
class Child extends Parent {
void display() { System.out.println("Child class method"); }
}
public class Main {
public static void main(String args[]) {
Child obj = new Child();
obj.show(); // Inherited method
obj.display(); // Own method
}
}
2. Method Overriding (Runtime Polymorphism)
Subclass provides its own version of a method already defined in the superclass.
- Condition: Method signature must be the same.
- Keyword: @Override (optional but recommended)
- Achieves: RP (Runtime Polymorphism)
Example:
class Parent {
void show() { System.out.println("Parent method"); }
}
