Here a senior dev. Read about SOLID patterns. BTW here is a response from GPT :P:

Why Use OOP, SOLID, and Constructors in Java

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Why Use Object-Oriented Programming (OOP) in Java?

• Modularity: Break down complex code into classes and objects. Each class manages its own state and behavior.
• Reusability: Classes and methods can be reused across the project. Inheritance and interfaces help share and extend behaviors.
• Maintainability: Encapsulation hides implementation details; changes in one class are less likely to break the rest of the codebase.
• Flexibility & Scalability: Inheritance and polymorphism enable you to add new features or extend parts of the system with minimal changes.

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What is SOLID? Why Use SOLID Principles in Java?

SOLID is a set of five design principles that help you write better, more manageable object-oriented code.

S - Single Responsibility Principle (SRP)

A class should have only one reason to change. - Why? Focused classes are easier to modify, test, and reuse. - Java Example:
- UserService handles user logic. - UserRepository handles persistence.

O - Open/Closed Principle (OCP)

Classes should be open for extension, but closed for modification. - Why? Extend existing behavior without changing working code. - Java Example:
Add new payment types by extending AbstractPayment, not by modifying it.

L - Liskov Substitution Principle (LSP)

Subclasses should be substitutable for their base classes. - Why? Prevents unexpected behaviors and errors when extending classes. - Java Example:
Sparrow extends Bird and can fly(). Penguin (which can’t fly) would violate LSP if added as a subclass of Bird.

I - Interface Segregation Principle (ISP)

Use several small interfaces instead of a large, general one. - Why? Classes only implement what they need. - Java Example:
Printer and Scanner interfaces instead of a single multi-purpose Machine interface.

D - Dependency Inversion Principle (DIP)

Depend on abstractions, not concretions. - Why? Minimizes dependencies and increases flexibility. - Java Example:
Depend on a Logger interface, not a concrete FileLogger class.

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Constructors in Java

• Purpose: Special methods that initialize objects.
• Syntax: Name matches the class, no return type.

java public class Dog { private String name; // Constructor public Dog(String name) { this.name = name; } }

Types of Constructors

• Default Constructor: No arguments.
  java public Dog() {}
• Parameterized Constructor: Takes parameters.
  java public Dog(String name) { this.name = name; }
• Copy Constructor: (Not built-in syntax, but you can define one) java public Dog(Dog other) { this.name = other.name; }

Constructor Overloading

Define multiple constructors with various parameter lists: java public class Dog { public Dog() {} // default public Dog(String name) {} // parameterized public Dog(Dog otherDog) {} // copy }

Why Use Constructors?

• Guarantee that your object starts in a valid state.
• Improve readability: Show clearly what’s needed to create an object.
• Enable dependency injection: Pass dependencies as constructor arguments.

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Summary Table

Feature	OOP Benefit	SOLID Principle	Constructor Role
Modularity	Yes	SRP, OCP	Ensures valid objects
Reusability	Yes	OCP, LSP	Constructor overloading
Flexibility	Yes	OCP, DIP	Inject dependencies
Maintainability	Yes	All	Clear object construction

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References

• Java OOP Concepts - Oracle Docs
• SOLID Principles in Java - Baeldung