J7 is in lower mid range price. n a7 is a upper mid range premium phone. There is a lot price differences in between j7 and a7. If you want just a big phone n good battery life then go for j7.
If you wan a premium and good looking phone with high screen quality and powerful then go for a7 but battery life will be 2 hours less then j7. j7 lack many functions.
I had used j7 for almost a month and found that it lacked many functions so I switch to a7. but I must say I like j7 battery life .