Solid Principle examples anywhere?

Question

We all write code with some patterns even when we dont realise it. I am trying to really understand some of the S.O.L.I.D principles and how you apply these

Answer 1

I am no expert like others but will give a shot at explaining DIP with concept. At the heart of DIP is program to an interface i.e. your high level classes will rely on abstraction and your low level classes rely on the abstraction as well. for example

Lets say you define an abstraction called PhoneVendor i.e it can be samsung, apple, nokia etc. Sorry about the code i haven't written Java for a while i.e it might have syntax error, but nonetheless its about the concept.

public abstract class PhoneVendor {

    /**
    * Abstract method that returns a list of phone types that each vendor creates.
    */
    public abstract Vector getPhones(){ }
}


public class Samsung extends PhoneVendor{
    public Vector getPhones(){ // return a list of phones it manufactures...  }
}

public class PhoneFinder{
   private PhoneVendor vendor;

   public PhoneFinder(PhoneVendor vendor){ this.vendor = vendor;}

  /**
   *for example just return a concatnated string of phones
  */
   public string getPhoneTypes(){
      Vector ListOfPhones = PhoneVendor.getPhones();        
      return ListOfPhones;
   }
}

As you can see PhoneFinder class depends on the abstraction not the implementation of the PhoneVendor. And your fundamental classes that implements the Abstraction are decoupled from the high level classes that use it. This makes the design really flexible where adding a new Low level classes wont break any previously written code since PhoneFinder is dependent on the abstraction not the implementation.