Composite pattern : Example 1

A component has many elements and itself which has many elements and itself, etc.

A file system is a typical example.

Directory is a composite pattern.

When you deal with Directory object, if isFile() returns true, work on file, if isDirectory() returns true, work on Directory object.

class Directory {

   Directory dir;

   File[] f;

   ...

   boolean isDirectory() {

       return f == null;

   }

   boolean isFile() {

       return f != null;

   }

   File getFile(int i) {

      if (isFile())

         return f [i];

      return null;

   }

   Directory getDirectory() {

      if (isDirectory())

          return dir;

      return null;

   }

   ....

}