What is SOLID? Provide examples of principles.

SOLID is a set of five principles of object-oriented programming aimed at improving the structure and maintainability of code:

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

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

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

4. I — Interface Segregation Principle: clients should not depend on interfaces they do not use.

5. D — Dependency Inversion Principle: high-level modules should not depend on low-level modules; both should depend on abstractions.

Example for Single Responsibility Principle:

class Report {
    public String generateReport() {
        // report generation logic
    }
}

class ReportPrinter {
    public void print(String report) {
        // report printing logic
    }
}

Here, report generation and printing are separated into different classes, each responsible for its own task.