local inner class vs anonymous inner class

[John Eipe]

Hi

I was reading Inner Classes

and came through 2 types of inner classes - local and anonymous.

Could someone explain the differences with a sample code?

Thanks.

[Abimaran Kugathasan]

Local inner class means, a class declared inside a method. And, anonymous means, a class created on the FLY.

[Campbell Ritchie]

There are examples of anonymous classes here, and in the older links mentioned.
A local class would look something like this

public void foo(Foo f1, Foo f2)
{
/**
 * A Comparator for Foos which compares by . . .
 */
   class FooComp implements Comparator<Foo>
   {
      public int compare(Foo f, Foo ff)
      {
         . . .
         return i;
      }
   }//end FooComp class

   myList.add(f1);
   myList.add(f2);
   Collections.sort(myList, new FooComp());
}

I'll let you work out how many bits of bad design there are in that code
[edit]Remove one erroneous } and new line from code[edit]

[Alex Hurtt]

In sticking with Campbell's example, an anonymous class would look like this:

public void foo(Foo f1, Foo f2) {
/**
 * A Comparator for Foos which compares by . . .
 */

      myList.add(f1);
      myList.add(f2);
      Collections.sort(myList,
                             new Comparator<Foo>() {
                               public int compare(Foo f1, Foo f2) {
                                   int someIntVal = //do comparison here.
                                   return someIntVal;
                               }
                             }
                            );
}

Difference here is you create an actual concrete implementation of the Comparator interface "on the fly" and give it no name/reference assignment. You can't refer back to it later or anything.
This can be useful if/when you have no other use for the Comparator outside the scope where it is used for example. It looks wierd at first to those who are not used to it because you are using the 'new' keyword to instantiate an Interface which you normally can't do except when you are making an implementation of it at the same time like this.

[John Eipe]

Thanks a ton!

Anonymous classes well explained!!!

[Campbell Ritchie]

You're welcome