SOLID Principles with Detailed Examples- Interview Question and Answer

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Jul 4, 2026

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Java interview and answers

SOLID is a set of 5 object-oriented design principles that help developers write clean, maintainable, reusable, and scalable code.

Think of SOLID as 5 rules for writing better Java classes.

Why do we use SOLID?

Without SOLID:

• Code becomes difficult to understand.
• Bug fixing becomes harder.
• Small changes affect many classes.
• Code cannot be reused easily.

With SOLID:

• Easy to maintain
• Easy to test
• Easy to extend
• Less bugs
• Better team collaboration

1. S — Single Responsibility Principle (SRP) :
   A class should have only one reason to change.

One class = One responsibility (One job).

Bad Example
This Employee class has multiple responsibilities:

• Stores employee data
• Calculates salary
• Saves data to a database
• Generates reports

class Employee {
    private String name;
    private double salary;

    public Employee(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }…