Normally one would just use BigInteger objects if one wanted to add together two integers with 1000 digits.
However I expect you are asking about some homework problem, in which case BigInteger wouldn't be acceptable. If that's the case, please read these links: DoYourOwnHomework and ShowSomeEffort, and then if you still have a question, don't hesitate to ask that question here.
posted 5 years ago
Keep the numbers as two int arrays. Traverse the arrays and add the numbers moving the 'carry' to the preceeding index. Finally print the array.