difference between hashmap and hashtable

Possible Duplicate:
Differences between HashMap and Hashtable?

I went to an interview the other day interviewer asked me under which situation will there be a problem to use hashmap rather then hashtable? Meaning give a eg where hashtmap use will result in problem but using hashtable will resolve the problem.

He told me that the machine in which the code is run is single core!!

I gave a eg

Time        Thread1            Thread 2
   t0    tb.put("a",1)       
   t1     tb.put("a",2)          int a = tb.get("a"); 

I told that if at t1 if both t1 and t2 executes simultaniously then it will result in problem. He said that since it is a single core cpu it will never execute 2 statements in parallel

Can someone please clarify that , when will there be a problem? Any example of situation?

EDIT:I posted the question by interchaing hashmap and hashtable.I know that hashtable method are synchronized and that of hashmap are not and i had told it to him

To experient i implemted following.And the code never crashed? I dint use hashtable but still it t is a hashmap in A :)

public class MyT extends Thread {

    HashMap<String,String > a = A.t;
    @Override
    public void run() {
        while (true) {
            a.put("a", "one");
            System.out.println(Thread.currentThread().getName());
        }
    }

    public static void main(String[] args) {
        MyT t1 = new MyT();
        t1.start();
        MyT t2 = new MyT();
        t2.start();
    }
}

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I think you have to do the following things first before asking:

Search on stackoverflow

Search on Google

The following results are obtained by above two methods:

StackOverflow: Differences between HashMap and Hashtable?

Google

what is the difference between HashMap and Hashtable

Difference between HashMap and HashTable? Can we make hashmap synchronized?

Hope that helps :)

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Unlike the new collection implementations, Hashtable is synchronized. That's why I could imagine a situation when using Hashmap would create a problem, and using Hashtable would resolve it.

The fact that it's single core is of no consequence: if Thread1 is pre-empted in the middle of a put call, Thread2 will see an inconsistent state, and may crash.

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Well, just because it's single core, doesn't mean you can't have race conditions. It possibly (probably?) means you won't have memory visibility issues, but you can certainly run multiple threads on a single core, and they can still be scheduled such that you get race conditions.

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