Help in defining the datastructures for a problem

Question

Hi there,
I am a newbie to Java programming and would like to get some feedback on how I can proceed with a problem I have at hand. I have to maintain the objects information in the memory for a SITE. SITE has side id, site name, and a site will be related to devices (one or more devices). Devices will have information such as is it alive what is the frequency of its alive signal coming to the server. These information have to be in-memory all the time so that at any point of time I would have to pick the device alive signal and process the neccesary tasks such as send an email to user whose device is not working. (email information for each device as well will be maintained in the memory). What kind of data structure can I use to acheive this scanerio. I was thinking of HASHTABLE but I am unable to get any samples that can explain the HASHTABLE usage. If anyone could help me in getting the right information it will be really helpful.
Thanking you in advance
regards
John

Answer 1

Hi,
This solution is based on few assumptions.
Hope u know abt a value object.
If u dont know, Value object is just a java class which contains few properties and getter and setter methods for getting and setting the values of properties. In ur case the value object may look like this.
public class Device {
private boolean alive;
public void setAlive(boolean alive) {
this.alive = alive;
public boolean getAlive() {
return alive;
and so on for all the properties u need to check for devices.
--> I think there will be only 1 device of a particular type. i.e., we will not be using 2 instances of the same device. Then for each device use a value object and set it properties and save it in HashMap with a name.
For example:
Let the device be Mortor(Just an example)
Device d = new Device();
d.setAlive(true);
and set all other properties.
Then put the object into HashMap as follows.
HashMap map = new HashMap();
map.put("Motor", d);
in the same way u can keep all ur devices with a name and value pair.
When ever u want to get that device, u can use as follows
Device d = (Device)map.get("Motor");
and u can work on the device "d" using getters.
in case if we want to use 2 instances of the same device then add the 2 instances to ArrayList and u can retrieve from arraylist when ever u want.
Hope I am clear
Regards
Karthik