Is it OK to have an 'empty' class that extends another class?

public class Foo {
  /* constructors, fields, method, logic and what-not */
}

public class Bar extends Foo {
  /* nothing here but constructors */
}

public class Bar {
  private Foo foo;

  /* constructors and a bunch of wrapper methods that call
     into foo */
}

public class Foo {
  /* constructors, fields, method, logic and what-not */

  private boolean isABar; // Could be an enum
}

if (foo instanceof Bar) {
    // Do Bar-specific things
}

class Bar extends AbstractFoo {
    public void specialOp() {
        // Do Bar-specific things
    }
}

// ...
foo.specialOp();

class FooBarImplementation
{
   public void doSomething() { /* etc. */ }
   /* etc. */
}

class Foo inherits FooBarImplementation { /* etc. */ }
class Bar inherits FooBarImplementation { /* etc. */ }

class FooBarImplementation
{
   public void doSomething() { /* etc. */ }
   /* etc. */
}

class Foo
{
   private FooBarImplementation fooBarImplementation = new FooBarImplementation() ;

   public void doSomething() { this.fooBarImplementation.doSomething() ; }
   /* etc. */
}


class Bar
{
   private FooBarImplementation fooBarImplementation = new FooBarImplementation() ;

   public void doSomething() { this.fooBarImplementation.doSomething() ; }
   /* etc. */
}

Class MainStuff;
Class TypeA;
Class TypeB;