Does anybody know a good tutorial or explanation on how to use Hashmaps in processing? I read the Reference and the example by Dan Shiffmann but I have to admit i still dont get the whole idea of how to use it.

Im working with the Carnivore example and they use a hashmap to store the different pakets. Maybe somebody can explain whats happening here regarding the Hashmaps.

Thx!

Code:

import java.util.Iterator;
import org.rsg.carnivore.*;
import org.rsg.carnivore.net.*;
import org.rsg.lib.Log;

HashMap nodes = new HashMap();
float startDiameter = 20.0;
pakets[]
 
float x, y;

void setup(){
  size(800, 600);
  ellipseMode(CENTER);

  Log.setDebug(true); // Uncomment this for verbose mode
  CarnivoreP5 c = new CarnivoreP5(this);
  //c.setVolumeLimit(4);
}

void draw() {
  background(255);
  drawNodes();
}

// Iterate through each node 
synchronized void drawNodes() {
  Iterator it = nodes.keySet().iterator();
  while(it.hasNext()){
    String ip = (String)it.next();
    println((String)it.next());
    float d = float(nodes.get(ip).toString());



 // Use last two IP address bytes for x/y coords
    
    String ip_as_array[] = split(ip, '.');
    x = int(ip_as_array[2]) * width / 255; // Scale to applet size
    y = int(ip_as_array[3]) * height / 255; // Scale to applet size
    
    
    
 // Use time
    
    String time_as_array[] = split(ip, '.');
    x = int(ip_as_array[2]) * width / 255; // Scale to applet size
    y = int(ip_as_array[3]) * height / 255; // Scale to applet size

    
    // Draw the node
    stroke(0);
    fill(color(100, 100, 100, 200)); // Rim
    ellipse(x, y, d, d);		 // Node circle
    noStroke();
    fill(color(100, 100, 100, 50));  // Halo
    ellipse(x, y, d, d);

    
   
  }  
}

// Called each time a new packet arrives
synchronized void packetEvent(CarnivorePacket packet){
 // println("[PDE] packetEvent: " + packet);
//println(packet.dateStamp());
  // Remember these nodes in our hash map
  nodes.put(packet.receiverAddress.toString(), str(startDiameter));
  nodes.put(packet.senderAddress.toString(), str(startDiameter));
}
 

Thast mostly what i found out by reading the tutorials and Wikipedia.
But I got more questions of the usage of it.
if have no clue what happens here :

Iterator it = nodes.keySet().iterator();

or what   while(it.hasNext()){ means.

here : String ip = (String)it.next(); what is next ?

I guess in my case it would be maybe easier to just use an Array cause all i want to do is to draw all the pakets I recieve in a linear way. Dont need to search for information within these pakets.

How can I change it to an array? Any help would be great.

As I wrote, Iterator allows to iterate on the nodes of the HashMap, ie. to enumerate them, to process them all.
A HashMap has no method returning an iterator (unlike some other Collections), but fortunately there is a way to get all keys at once (keySet() method), and you can iterate on the result.
it.hasNext() checks if the iterator has walked all the values. It returns false if all keys have been iterated. it.next() allows to get the next value.
All this is roughly equivalent to a for() loop, if you want, something like
for (Iterator it = nodes.keySet().iterator(); it.hasNext(); it.next())
except that it.next() is also equivalent to ip = map[it] (pseudo-code!).

A simple array might not be suited to your needs, as the size won't adapt to the amount of data. If fixed size fits your needs, that's OK then.
Otherwise, you might also use an ArrayList.
Note that HashMap here has the side effect to erase/update the previous values. If you don't need this property, indeed you can use another data storage.

I took a closer look at the programm itself and there are still some things unclear to me. But maybe thats the probleme and not the hashmap itself.


 nodes.put(packet.receiverAddress.toString(), str(startDiameter));
 nodes.put(packet.senderAddress.toString(), str(startDiameter));

this is the part where information is stored in the Hashmap. right?
the first is the key, the second the value. so the reciever and sender ip adress is stored with the value of the startDiameter? And how do i know they belong together? And what if i want to also save the time the paket was recieved. Using arrays i know that i just create a different array, and there i know, same index, means same paket.
How do i do it with a hashmap ? create a different hashmap and use the same key?  thats the part where i am confused cause

So to summarize the whole programm.
It creates a node for every ip adress and gives it the value of the diameter that updates during time. Am i right if i say that the programm overwrites a node as it has the same ip adress? so there is only 1 node for every ip adress?

I guess thats not what i want. I want a programm that leaves a mark on a timeline like graph everytime a packet is recieved. size and color of the mark should be changed by type etc.

So would it make sense to creat a class where i store all the informations of a recieved paket like, time, reciever and sender and so on? and use an array list to expand the list of objects ? so that i get an growing arraylist of objects containing all information of the recieved paket?


Thx again guys!

big thanks tanepierre for answering all my questions. Seems like i wasnt that wrong. guess the problem was that i just wanted something else then the example did.

But i realized that it is even much easier and has alot of benefits to just parse the txt log fill carnivore can output then creating a graph in realtime.
Thanks again for the help Guys!