In object-oriented programming (OOP), there are many helpful rules and ideas for writing better code. Five important ones are grouped together and called SOLID. Each rule teaches something different, but they also work together — following one often helps with the others too. In this article, we’ll learn what SOLID principles mean and how they work in Java.

History of SOLID Principles in Java

A programmer, Robert C. Martin, developed five significant rules to write improved code, and they are referred to by the acronym "SOLID." When you implement all these SOLID rules simultaneously, it assists you in creating software that is simpler to understand and maintain.

Some advantages of implementing SOLID are:

• It prevents muddled or ambiguous code.

• You can correct or enhance code quickly.

•  It helps make software faster and easier to improve.

What Is S.O.L.I.D?

SOLID are the names of five significant Java programming rules. Each of the letters in the word SOLID stands for one rule:

S – Single Responsibility Principle

O – Open-Closed Principle

L – Liskov Substitution Principle

I – Interface Segregation Principle

D – Dependency Inversion Principle

Single Responsibility Principle in Java

What is it?

Robert C. Martin states that a class (a chunk of code) should only have one primary responsibility.

Under this rule, there must be only a single reason to modify a class. When a class performs more than one function, it gets confusing and more difficult to repair or maintain.

Let us consider an example:

Let's say you have a class that:

• Accesses a database

• Reads from the database

• Writes that information to a file

This class is doing too much. If we ever need to alter the method it uses to connect to the database, or how it writes to a file, we have a number of reasons to do so.

A better approach:

• take care of database work in one class

• do file writing in another

Some simpler examples follow:

• A Car class can move the car on and off. But washing the car should be performed by a Car Wash class.

• A Book class holds the book’s title and the words inside it.

Why Do We Need This Principle?

When we use the Single Responsibility Principle, it becomes easier to test. That's because the class only performs one task, so there are fewer things to be tested. Additionally, with less to do, the class does not rely on many other classes.

Open-Closed Principle in Java

Open-Closed Principle is one of SOLID principles in Java. this is to say that you ought to be in a position to introduce new features or functions to a class without modifying its old code. Take, for instance, the case where you have a class that performs calculations, and you need to introduce new types of calculations. You ought to be able to accomplish it by introducing new code and not by modifying the old code.

Why Is This Principle Needed?

The Open-Closed Principle is necessary because there are times when we borrow classes from other libraries or code from someone else. We ought to have the ability to add functionality to these classes without modifying the initial code. But if we only implement inheritance (creating a new class based on an existing one), we may rely too heavily on the workings of the previous class.

Liskov Substitution Principle in Java

The Liskov Substitution Principle states that a child class should be substitutable with its parent class without issues. Robert C. Martin came up with this concept. It might sound confusing to begin with, but it's really straightforward. If a class is a child (or subclass) of a class, it should behave like the parent class in every situation.

Why Is This Principle Needed?

The Liskov Substitution Principle assists us in employing inheritance properly. It keeps reminding us that a child class must actually be a type of the parent class. That is the "is-a" relationship. A square may appear to be a type of rectangle, for instance, but that is not necessarily the case. Rectangles can have varying lengths and widths, whereas squares have all sides of equal length.

Dependency Inversion Principle

The Dependency Inversion Principle is a rule by Robert C. Martin. He states that code must rely on general concepts (referred to as abstractions), not specific details. High-level components of a program (the major stuff) cannot depend directly on low-level components (the minor details).

Here's an example:

Imagine you go to a shop and want to pay with your debit card. The cashier doesn’t care if it’s a Visa or a MasterCard. They simply swipe it into the machine. Both you and the cashier rely on the concept of a "card," regardless of the brand.

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Conclusion:

The SOLID principles are a set of five significant guidelines that assist programmers in writing neat, minimal, and easy-to-maintain code in Java. Every principle guides us in some new manner to make our code better, such as having a single job per class, being able to implement new features without modifying existing code, and ensuring child classes behave exactly like parent classes. These concepts might sound technical, but they play a significant role in actual coding.

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