Casting for HashMap

Question

Hi,
I have a class called ThreadInfo:
public class ThreadInfo{
          public ChatWindow threadID;
          public String ip;
          public String username;
          public boolean windowOpen;
          public boolean linkEstablished;
          ThreadInfo(){
               windowOpen = false;
               linkEstablished=false;
     }I also have a class:
public class ServerStatus {
     private HashMap threadList;
     ServerStatus() {
          threadList = new HashMap();
}now if I want to put a value in the HashMap, I would do:
public void insertNewThread(String key, ThreadInfo info) {
          threadList.put(key,info);
     }right?
and about retrieving a value, does this sound correct?
public ThreadInfo getThread(String key){
          ThreadInfo requiredInfo = (ThreadInfo)threadList.get(key);
          return requiredInfo;
          }My query is really about this casting thing because in the API the get method returns an object, but since I know I am inserting a ThreadInfo class instance in the map, I thought that the casting here would give me the correct result.
any insight to this is highly appreciated
thanks,
Talal

Answer 1

Be careful doing this.
HashMap can contain null as a value. null cannot be
cast. Therefore you might want to test the value
returned by get(key) for null before trying to cast it
to your return type.
matfudI do not believe the above is correct.
Example:
import java.util.*;
public class Test68 {
    public static void main(String[] args) {
        HashMap hm = new HashMap();
        hm.put("aaa", null);
        String s = (String)hm.get("aaa");
        System.out.println(s);
        ArrayList al = (ArrayList)null;  // And just for the fun of it
}C:\j2sdk1.4.0\Test>javac Test68.java
C:\j2sdk1.4.0\Test>java Test68
null
C:\j2sdk1.4.0\Test>