Here's my 2 cents:
1)I am a beginner in JAva and related technologies,does one need to be an expert in java to understand CQ5?
2)I have mainly worked on Teamsite CMS before,how easy is it for someone from that background to adapt to DAY CQ/
Any previous CMS knowledge is definintely helpful. Teamsite is VERY different to CQ. However, the goal is the same. Content authors need a way of entering content that ultimately gets displayed and served up as a web page. Teamsite does this with forms whereas CQ does this more inline on the page... If you've ever worked with Teamsite Sitepublisher, that's even better. Either way, having CMS experience is definitely helpful.
Thanks for your detailed reply
I will be getting trained on DAY CQ 5 shortly and as per your reply ,i think it will help me in getting started.