code: public Enumeration<NetworkInterface> getSubInterfaces() {
          class subIFs implements Enumeration<NetworkInterface> {
  
              private int i=0;
  
              subIFs() {
              }
  
              public NetworkInterface nextElement() {
                  if (i < childs.length) {
                      return childs[i++];
                  } else {
                      throw new NoSuchElementException();
                  }
              }
  
              public boolean hasMoreElements() {
                  return (i < childs.length);
              }
          }
          return new subIFs();
  
      }
docs: Get an Enumeration with all the subinterfaces (also known as virtual
  interfaces) attached to this network interface.
  <p>
  For instance eth0:1 will be a subinterface to eth0.
  
  @return an Enumeration object with all of the subinterfaces
  of this network interface
  @since 1.6