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Index › Programming Questions & Help › Syntax Questions › Hash Table Structure

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Hash Table Structure? (Read 960 times)

smhall05

Hash Table Structure?
Jun 13^th, 2008, 11:03pm

Is it possible to create a hash table in Processing? If that is not the correct term, here is what I want. I want to be able to quantify the number of objects in a list/array on the fly. So if my list/array consists of ip addresses:

209.241.119.228
141.211.250.129
97.102.93.122
97.102.93.122
208.54.94.15

I want to create the below structure where the ip addresses are the indices and the content of the index is the number of collisions so to speak, how many times that ip address occurs.

[209.241.119.228] "1"
[141.211.250.129] "1"
[97.102.93.122] "2"
[208.54.94.15] "1"

antiplastik

Re: Hash Table Structure?
Reply #1 - Jun 14^th, 2008, 12:45am

what you want is called (in Java) a HashMap. that's how associative arrays are implemented in Java.

here is the java doc:
http://java.sun.com/j2se/1.4.2/docs/api/java/util/HashMap.html

and a simple example showing how to add elements
Quote:

HashMap hm = new HashMap();
String ip = "192.168.0.1";
Integer count = new Integer(1);
hm.put(ip, count);
// you can't put primitives in a HashMap, objects only.
// that's why I've used an Integer and not an int.

Jo Wood

Re: Hash Table Structure?
Reply #2 - Jun 14^th, 2008, 4:56pm

Actually, if you are using Java 1.5 or above, Java 'autoboxing' will silently convert between Number classes and their primitives. This means you can add and remove normal primitive numbers to a HashMap:

Code:


HashMap hm = new HashMap(); 
String ip = "192.168.0.1"; 
int count=1;
hm.put(ip, count);

This can make the code for manipulating HashMaps a little simpler:

Code:


String newIP = "192.168.0.1";

if (hm.containsKey(newIP))
{
  count = (Integer)hm.get(newIP);
  hm.put(newIP,++count);
}

Once (or if) Processing can accept Java 1.5 syntax and above, the code can be made even simpler (and safer) using generics.

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