Cohesion

Cohesion refers to how closely related and focused the responsibilities of a module/class are. It measures how well the methods inside a class are related to each other.

High Cohesion

A class has a well-defined purpose with related methods.

class ReportPrinter {
    void printReport() {
        System.out.println("Printing report...");
    }
}

class EmailSender {
    void sendEmail() {
        System.out.println("Sending email...");
    }
}

class TaxCalculator {
    void calculateTax() {
        System.out.println("Calculating tax...");
    }
}

Explanation

• Each class has a single, well-defined responsibility, making the system easier to understand, test, and modify.
• This approach follows high cohesion and SRP.

Low Cohesion

A class does too many unrelated tasks, making it difficult to maintain.

class Utility {
    void printReport() {
        System.out.println("Printing report...");
    }

    void sendEmail() {
        System.out.println("Sending email...");
    }

    void calculateTax() {
        System.out.println("Calculating tax...");
    }
}

Explanation

• This class handles printing, emailing, and tax calculations—unrelated responsibilities.
• If we need to modify one function, the others might be affected.
• The Single Responsibility Principle (SRP) is violated.