Hashtable concurrency !!!

Question

Hai....
Hashtable is thread safe. My doubt is if we put different objects in a Hashtable, whether its possible to access different objects from same table at a time.
ie :
Hashtable table = new Hashtable();
MyClass obj1     = new MyClass();
MyClass obj2     = new MyClass();
MyClass obj3     = new MyClass();
table.put( "1", obj1);
table.put( "2", obj2);
table.put( "3", obj3);Can two threads access the table at a time safely ?
Thread--1
table.get("1");
Thread--2
table.get("2");Can thread-1 and Thread-2 run the above code safly ?
Ie : Whether the Hashtable object or objects inside the table is thread safe ?
I think you got my question.
Thanks
Nikhil.k.r

Answer 1

The Ht is threadsafe. That means that any of its methods can be called concurrently with any other of its methods without causing problems.
However:
* It does NOT mean the the objects inside are threadsafe. If two threads call get() at the same time, one will be blocked while until the other's get() completes. But once the get()s have completed, you're not sycned anymore, so those two threads can do whatever they want to the objects retrieved, and ther will be no protection. If you need protected, then apply propert syncing to the obejcts.
* If you're iterating over Ht's keySet(), entrySet() or values() Collection, then you have to sync around the whole iteration like so: synchronized (myHashtable) {
    Set set = entrySet();
    for (Map.Entry entry : set) {
        // do stuff with entry
} Also, you should be using HashMap rather than Hashtable, and Collections.synchronizedMap if you need synchronization.