title: Relationships between classes that implement same interface
body: <p>I'm pretty much java beginner, and i've come to ask stackoverflow forum for one simple question. I already checked similar question here on SO, but i didn't found the desired answer, LINK: <a href="https://stackoverflow.com/questions/1050146/is-there-any-relation-between-the-class-that-implements-interface-and-that-inter">Is there any relation between the class that implements interface and that interface?</a></p>
  
  <p>We know if <em>Cat</em> extends <em>Animal</em>, there is a relationship here. So Cat is-a Animal ( but not necessarily otherwise. Animal is also a Dog..). We know this relationship as "is-a" - <strong>inheritance</strong>.</p>
  
  <p>If we have another two classes: <em>Girl</em> and <em>Candy</em> and if class Girl holds instance of Candy, then we name this relationship "has-a"-<strong>composition</strong>, because we can say that Girls has-a Candy.</p>
  
  <p>Correct me if i made something wrong with above examples.</p>
  
  <p>Anyway my question is if its there some relationship between objects of classes that implement the same interface? Let's say:</p>
  
  <pre><code>public class A implements InterfaceA {}
  
  public class B implements InterfaceA {}
  </code></pre>
  
  <p>If there is some relationship, how we can make use of that relationship? Thanks for your answers in advance..</p>
  
  <p>EDIT: For those who think that there isn't a relationship, i have a book "java how to program ninth edition" and there is a UML diagram which shows classes that implements same interface in "relationship" ?</p>
  
  <p>Image:</p>
  
  <p><img src="https://i.stack.imgur.com/HWeMA.png" alt="enter image description here"></p>