---------------------------------- Data.java
import java.time.LocalDate;
class Data {
  int value;          //value of transmitted data
  LocalDate time;     //time of sending/receiving
  Data(int value) {
    this.value = value;
    this.time = LocalDate.now();
  }
}
---------------------------------- Network.java
import java.time.LocalDate;
class Network {
   class Node {
    char id; //Node identifier
    final Node[] ports; // array of nodes the node is connected to
    Node(int size, char id) {
        this.ports = new Node[size];
        this.id = id;
    }
    boolean send(Data data, int port) { //sends data to node on specified port
      if (ports[port] == null) return false;
      ports[port].receive(data); // data sent by calling receive from receiver node
      return true;
    }
    int broadcast(Data data) { //sends datagram to all ports to which a Node is connected
      for (int i = 0; i < ports.length; i++) {
        if (ports[i] != null) send (data, i);
      } return data.value;
    }
    void receive(Data data) { //when Node receives data, it logs the event to the console
          data.time = LocalDate.now();
          System.out.println("Node " + id +" has received one transmission with content "+ data.value + " on " + data.time.toString());
       }
   }
}
---------------------------------- Main.java
public class Main {
  public static void main(String[] args) {
    //build Network
    Network n = new Network();
    Node nodeA = n.new Node(3, 'A');
    Node nodeB = n.new Node(3, 'B');
    Node nodeC = n.new Node(3, 'C');
    //connect nodes
    nodeA.ports[0] = nodeB;
    nodeA.ports[1] = nodeC;      
    nodeB.ports[0] = nodeC;        
    nodeC.ports[0] = nodeA; 
    //create Data
    Data fromA = new Data(1906); //Birth year of Grace Hopper
    Data fromB = new Data(1912); //Birth year of Alan Turing
    Data fromC = new Data(1815); //Birth year of Ada Lovelace
    //broadcasts: send Data to all connnected nodes
    nodeA.broadcast(fromA);
    nodeB.broadcast(fromB);
    nodeC.broadcast(fromC);
  }
}
 What is the issue that prevents this code from working (assume that all classes are in the same package)?
 1) We cannot simply access the ports array using the indices - we would need an Iterator to get the values in the array.
 2) Node is an inner class of Network - in order to use it as a data type in Main, we need to refer to it as Network.Node. 
 3) Broadcasts cannot work as the ports array contents is not visible.
 4) It is not possible to define class Node within the scope of the class Network.