Question

For example is it more efficient to use NSInteger or int when defining variables?

In Java, is it more efficient to use Integer or the int primitive data type?

Answer 1

NSInteger is not an object, it is simply a synonym that makes ints platform independent as you can see from the definition:

#if __LP64__ || NS_BUILD_32_LIKE_64
  typedef long NSInteger;
  typedef unsigned long NSUInteger;
#else
  typedef int NSInteger;
  typedef unsigned int NSUInteger;
#endif

NSNumber, however, is an object type. You would e.g. use it when you need to store numbers in an NSArray. If you are doing calculations or indexing, NSInteger will be easier to work with and also more efficient.