This is just another way of viewing the SOLID design principles very very shortly 🙂

• S: Methods with no more than 5 lines of code,
  classes with no more than 3 public methods (average).
• O: If it works, don’t touch it (extend it)
• L: Don’t abuse inheritance (are they really the same thing?)
  
• I: This one was placed here to form the word “solid”
  but it’s the same as S.
• D: Never create the instance of the dependency inside the object
  which uses it.