{"id":420,"date":"2020-08-05T18:22:48","date_gmt":"2020-08-05T12:52:48","guid":{"rendered":"https:\/\/saurabhjain1537.wordpress.com\/?p=420"},"modified":"2025-02-27T07:46:42","modified_gmt":"2025-02-27T07:46:42","slug":"solid-principles-single-responsibility","status":"publish","type":"post","link":"https:\/\/saurabhjain.dev\/?p=420","title":{"rendered":"SOLID Principles: Single Responsibility"},"content":{"rendered":"\n

Introduction<\/strong><\/p>\n\n\n\n

SOLID Design Principles are tips and tricks to organize the code in different classes which helps in keeping the code clean, maintainable and scalable (or extensible).<\/p>\n\n\n\n

The way software modules & classes are designed & organized have a major impact on the people associated with it:<\/p>\n\n\n\n

  1. Programmers: The application can be easy to manage and extends.<\/li>
  2. Business owners: The application can be quickly enhanced to add business critical and compliance mandatory functionalities.<\/li>
  3. Users: The application can provide improved experience and help achieve more.<\/li><\/ol>\n\n\n\n

    The Single Responsibility Principle “S”<\/strong><\/p>\n\n\n\n

    As the name suggests, a class should be responsible for one and only one thing. In words of Robert C. Martin “A class should have only one reason to change”.<\/p>\n\n\n\n

    Although it seems pretty obvious & it is basic Object Oriented Design, but still it gets defied many times.<\/p>\n\n\n\n

    Consider this example of LogManager<\/strong> class having a field Enum LogType<\/strong> with possible values of FileBased, DBBased:<\/p>\n\n\n\n

    \"\"
    Figure 1<\/figcaption><\/figure><\/div>\n\n\n\n

    The log()<\/em> method converts Object to string and logs the string to File or DB conditionally:<\/p>\n\n\n\n

        void log(Object obj) {\n\n      String message = convertToJson(obj);\n\n      switch(logType) {\n        case FileBased:\n          logToFile(message);\n          break;\n\n        case DBBased:\n          logToDB(message);\n          break;\n      }\n\n    }<\/code><\/pre>\n\n\n\n
    The purpose of above code is to perform logging, it seems to be doing fine by logging into a File or DB and it includes some helpers like converting an Object to JSON string.<\/p>\n\n\n\n
    However, this class has two reasons to change:<\/p>\n\n\n\n
    1. Changes in the way messages are logged<\/li>
    2. Changes in the way String is created<\/li><\/ol>\n\n\n\n
      In future, it may be decided to log messages as xml or csv or any other format. OR a different library may be used for converting Object to json string. But it should not impact the way strings are being persisted to storage (either File or DB).<\/p>\n\n\n\n
      Doing multiple things in a single class makes it tightly-coupled:<\/p>\n\n\n\n