A class should have only one reason to change.

Example: Consider a class that handles both user data and its formatting. This violates SRP.

// Violation of SRP
public class User {
    private String name;
    private String email;

    public User(String name, String email) {
        this.name = name;
        this.email = email;
    }

    // Responsibility 1: Managing user data
    public String getName() {
        return name;
    }

    public String getEmail() {
        return email;
    }

    // Responsibility 2: Formatting user data
    public String getUserDetails() {
        return "Name: " + name + ", Email: " + email;
    }
}

// Following SRP
public class User {
    private String name;
    private String email;

    public User(String name, String email) {
        this.name = name;
        this.email = email;
    }

    public String getName() {
        return name;
    }

    public String getEmail() {
        return email;
    }
}

public class UserFormatter {
    public String formatUserDetails(User user) {
        return "Name: " + user.getName() + ", Email: " + user.getEmail();
    }
}

Here, the User class handles only user data, while UserFormatter handles formatting. This separation ensures each class has only one reason to change.

Next: Open/Closed Principle (OCP)

SOLID