Hey my name is harikrishna i had ordered a ipad online whixh i was charged and the next minute i canceled it but i still not have got any refund

Apple do not charged you until it's delivered.

Even if the payment was processed, the refund will take several days to be processed. That is how banks work - they will process a refund within 5 days usually.

As for the charge, Apple processed my recent orders immediately and the charge appeared when the item was shipped.

I don't think this is so. Apple will charge you when the goods are dispatched. If they have stock that could mean an immediate charge as Babowa experienced.