title: How do I group many interfaces into a common single interface?
body: <p>EDIT: The simple answer to my question is that Java allows one interface to extend multiple other interfaces. This is what answers my logical question of how you group interfaces together in a common interface. This answer did not appear in the dupe question. Also the question was different, it was not about creating interface groups.</p>
  
  <p>Is there a reason in Java you cannot define one interface as implementing other interfaces? The answer I've seen and been dissatisfied with is that "interfaces themselves don't contain implementation, so how could an interface implement other other interfaces?" Well, that's a weak answer in my opinion, because its more a nod to English semantics than it is logical interpretation of the scenario. The logical interpretation of the scenario is since we can define classes to implement many interfaces, why can't we define an interface that itself represents a collection of interfaces.</p>
  
  <p>Suppose you have many classes that you want to each implement a large, common set of many interfaces. As it currently stands, you'd have to explicitly write out the list for each class. This means that if later you had to add another interface to your list of many, you'd have to modify each class. Having all the interfaces consolidated in one "super interface" would allow the programmer to make the change in only one place.</p>
  
  <p>And before you answer "make an abstract superclass that implements the list of interfaces, and have all your subclasses extend that superclass", keep in mind you cannot assume these classes do not already extend classes. One of the whole benefits of the implements keyword is so that you can adapt a class without having to change its taxonomy, right?</p>
  
  <p>I guess the long story short is: Why can't programmers define interfaces that are just groups of other interfaces? Or, maybe the better question is: If I can't define an interface as implementing other interfaces, HOW can I define interfaces that are groups of other interfaces?</p>
  
  <p>For those of you that prefer code, what I'm asking is why instead of doing this...</p>
  
  <pre><code>public class Foo extends ParentClass1 implements IBar1, IBar2, IBar3{
  }
  
  public class Baz extends ParentClass2 implements IBar1, IBar2, IBar3{
  }
  </code></pre>
  
  <p>...wouldn't it make more sense for Java to allow this:</p>
  
  <pre><code>public interface IAllBar implements IBar1, IBar2, IBar3{
  }
  
  public class Foo extends ParentClass1 implements IAllBar{
  }
  
  public class Baz extends ParentClass2 implements IAllBar{
  }
  </code></pre>
  
  <p>That way, later, if I create IBar4 I only have to modify IAllBar.java instead of Foo.java AND Baz.java.</p>
  
  <p>Edit: So according to below answers I can define IAllBar to EXTEND all those interfaces and I'll get exactly what I want. I'm glad some people are willing to read an entire post before jumping to the bottom to post mean responses.</p>