Demystifying the SOLID Principles for Writing Flexible Java Code

As Java developers, we juggle maintaining robust, adaptable codebases while also shipping new features. Things can get messy fast without some guardrails. That’s where the SOLID principles come to the rescue!

These five principles aren’t commandments etched in stone. They’re tried and tested practices that help tame the complexity of changing requirements. Think of SOLID as your compass for building Java applications that stand the test of time.

Let’s explore these principles in plain English with some handy examples:

Single Responsibility Principle

Ever struggled to find where a certain method lives in a 1000 line god class? That’s the Single Responsibility Principle knocking.

SRP says: a class should focus on one and only one job. When a class takes on too many duties, it becomes a nightmare to change.

Imagine a Bakery class that handles baking, pricing, reporting, HR and so on:

public class Bakery {

  public void bake() {
    // baking logic
  }
  
  public void setPrices() {
    // pricing logic
  }  

  public void generateReport() {
    // reporting logic
  }

  public void manageEmployees() {
    // HR logic
  }

}

Now we better add some new flour types! Where do we even start in this hot mess?

Instead, we could separate the duties:

public class BakeryProducts {…