The Single Responsibility Principle (SRP)

This principle says that a class should have one, and only one, reason to change.³

Here’s an example of the overlap between these design principles that was mentioned above: SRP, the first principle about encapsulation, and DRY all say similar, but slightly different things. Encapsulation is about abstracting behavior and putting things in your design that are likely to change in the same place. DRY is about avoiding duplicating code by putting identical behaviors in the same place. SRP is about designing your classes so that each does just one thing, and does it very well.

Every object should have a single responsibility and all the object’s services are targeted towards carrying out that responsibility. Each class should have only one reason to change. Put simply, this means to beware of having your class try to do too many things.