Core Java OOPs: Enterprise Implementation

Java is strictly object-oriented (mostly). In large systems, we use OOPs not just for organization, but for Decoupling and Polymorphism.

Inheritance and Interfaces

In Java, a class can only extend one superclass (Single Inheritance) but can implement multiple interfaces.

• Abstract Class: Use when you want to share code among several closely related classes.
• Interface: Use to define a contract. Modern Java (8+) allows default and static methods in interfaces.

java code
public interface PaymentGateway {
    void process(double amount);
    
    default void logTransaction(String id) {
        System.out.println("Logging: " + id);
    }
}

Polymorphism: Static vs Dynamic

• Static (Method Overloading): Handled at compile time. Same method name, different parameters.
• Dynamic (Method Overriding): Handled at runtime. Subclass provides a specific implementation of a method already defined in its parent.

Encapsulation & Records

Encapsulation (using private fields and public getters/setters) protects the internal state. In Java 14+, use records for immutable data carriers.

java code
// Modern Java Record
public record User(String id, String email) {}

Composition over Inheritance

Industry experts prefer composition (having an instance of another class) over inheritance. It's more flexible and avoids the "Fragile Base Class" problem.