DEV Community

Jack Lin
Jack Lin

Posted on

Single-Responsibility Principle (SRP)

If a class has too many responsibilities (High Cohesion), all classes that depend on this class have to be modified when we want to add a new feature to the class, which increases the difficulty of maintenance.

Here is an example, first define the data structure of an order, which can be output by a photocopier.

public class Order
{
    private string id;
    private double price;

    public void Print()
    {
        ...
    }
}
Enter fullscreen mode Exit fullscreen mode

Analyze class Order, it should only focus on processing the information of an order, Print() seems to be beyond its responsibility. Suppose there is a new requirement: export as PDF, then Order will be modified as:

public class Order
{
    private string id;
    private double price;

    public void Print()
    {
        ...
    }

    public void PrintByPdfExporter()
    {
        ...
    }
}
Enter fullscreen mode Exit fullscreen mode

At this point, all code that call to Print() must then be rewritten to be compatible with PrintByPdfExporter(). That's not a good practice when we calls Print() a lot in our code.

Now we apply the SRP principle to Order. Define an interface called IPrinter, then let PdfExporter and Printer implement IPrinter:

public interface IPrinter
{
    void Print(string id, double price);
}

public class PdfExporter : IPrinter
{
    public void Print(string id, double price)
    {
        ...
    }
}

public class Printer : IPrinter
{
    public void Print(string id, double price)
    {
        ...
    }
}

public class Order
{
    private string id;
    private double price;
    private IPrinter printer;

    public Order()
    {
        this.printer = new PdfExporter();
        // this.printer = new Printer();
    }

    public Print()
    {
        this.printer.Print(this.Id, this.Price);
    }
}
Enter fullscreen mode Exit fullscreen mode

This way, all changes related to printing orders are confined to individual IPrinter implementations. We only need to modify the contructor of Order or use dependency injection to decide what printer we what to use.

Heroku

Build apps, not infrastructure.

Dealing with servers, hardware, and infrastructure can take up your valuable time. Discover the benefits of Heroku, the PaaS of choice for developers since 2007.

Visit Site

Top comments (0)

A Workflow Copilot. Tailored to You.

Pieces.app image

Our desktop app, with its intelligent copilot, streamlines coding by generating snippets, extracting code from screenshots, and accelerating problem-solving.

Read the docs