#SRP SINGLE RESPONSIBILITY PRINCIPLE CODE#

Further refactoring of this example is necessary to achieve compliance with the other four principles.Uncle Bob states in his book that this might be one of the least understood principles.

#SRP SINGLE RESPONSIBILITY PRINCIPLE CODE#

NB: The refactored example code below breaks other SOLID principles in order that the application of the SRP is visible. The one reason for the class to change is if the alerting system is updated. Again, the OxygenMeter dependency is injected. This displays an alert that includes the current oxygen saturation level. The final class is named 'OxygenAlerter'. The only reason for the class to change is if the test process is changed. The method is the same as the original version except for the addition of a parameter that injects an OxygenMeter object containing the saturation level to test. This class includes a single method that compares the oxygen level with the minimum acceptable value. The second class is named 'OxygenSaturationChecker'. The other methods are removed so that the only reason for change is replacement of the monitoring hardware. In this case we will keep them together as they are closely related. You could decide to split these members into separate classes. This retains the OxygenSaturation property and the ReadOxygenLevel method. To refactor the code we will separate the functionality into three classes. Finally, if the alerting requirements become more sophisticated than outputting text to the console, the ShowLowOxygenAlert method will need to be rewritten. If the process for determining low oxygen is changed, perhaps to include a temperature variable, the class will need updating. If the oxygen monitoring hardware is replaced the ReadOxygenLevel method will need to be updated. There are at least three reasons for change within the OxygenMeter class. The 'ShowLowOxygenAlert' shows a warning that contains the current saturation value. The second method, 'OxygenLow', checks the oxygen saturation to ensure that it exceeds the minimum level of 75%.

It converts the value to a percentage and stores it in the OxygenSaturation property. The class includes a method named 'ReadOxygenLevel' that retrieves a value from a stream generated by the oxygen monitoring hardware. The code above is a class that communicates with a hardware device to monitor the oxygen levels in some water. Public double OxygenSaturation %)', OxygenSaturation) To demonstrate the application of the SRP, we can consider an example C# class that violates it and explain how the class can be refactored to comply with the principle: It can also make it easier to modify the overall software, either by extending existing classes or introducing new, interchangeable versions. Along with the other principles this permits looser coupling. As the classes perform only one duty, multiple classes will work together to achieve larger tasks. This reduces the need for changes so the code is less fragile. The creation of classes that are tightly focussed on a single purpose leads to code that is simpler to understand and maintain.Ī further benefit of having small, cohesive classes is that the chances of a class containing bugs is lowered. The number of classes present in a solution may increase accordingly so it is important to organise them well using namespaces and project folders. One key change is that the classes in your projects become smaller and cleaner. It may also be that multiple classes will require updates.Īpplication of the SRP can change your code considerably. It may be that when the one reason to change occurs, multiple members of the class may need modification. There may be many members as long as they relate to the single responsibility. It does not mean that your classes should only contain one method or property. Everything in the class should be related to that single purpose.

This means that every class, or similar structure, in your code should have only one job to do.

The Single Responsibility Principle (SRP) states that there should never be more than one reason for a class to change. Previous: The SOLID Principles The Principle

Srp single responsibility principle