The Irish striker said: "I was involved in both of the Republic of Ireland games at the end of the season, and I think playing international football can only benefit me.
"It's great to be able to test yourself at that kind of level. It makes you a better player and hopefully Sunderland will reap the benefit from that next season.
"I'm starting to get more and more involved in the Ireland set-up, and that's something I want to build on in the future. International football and club football can go hand in hand. If I'm playing well for Ireland, it'll give me more confidence when I pull on a Sunderland shirt. And if I'm doing well for Sunderland, I'm more likely to get a chance with my country."