Getting ScreenName using four access tokens



I have Valid twitter access tokens and consumer tokens in handy.
I want to get twitter screenname using those tokens.
Right i am doing this way
AccessToken a = new AccessToken(accessToken, accessSecret);
final Twitter twitter = new TwitterFactory().getInstance();
twitter.setOAuthConsumer(consumerKeys[0], consumerKeys[1]);
screenName = twitter.getScreenName();

But it is throwing verification exception? Is it possible to get screenname using those 4 tokens?
If so Can someone help me .

Thanks & Regards,