Tell about the SOLID principles.

SOLID principles are a set of five fundamental principles of object-oriented programming aimed at creating flexible, extendable, and maintainable code:

1. S — Single Responsibility Principle Each class should have only one reason to change, meaning it should be responsible for a single specific task.

2. O — Open/Closed Principle Software entities should be open for extension but closed for modification.

3. L — Liskov Substitution Principle Subclass objects should be interchangeable with superclass objects without affecting the correctness of the program.

4. I — Interface Segregation Principle Clients should not depend on interfaces they do not use. It's better to have several specific interfaces than a single universal one.

5. D — Dependency Inversion Principle High-level modules should not depend on low-level modules. Both should depend on abstractions.

Example in Java for the Single Responsibility Principle:

class Report {
    String content;
    // Responsible only for report data
}

class ReportPrinter {
    void print(Report report) {
        // Responsible only for outputting the report
        System.out.println(report.content);
    }
}

This separation of responsibilities makes the code easier to maintain and extend.