Long vs Integer, long vs int, what to use and when?

Long is the Object form of long, and Integer is the object form of int.

The long uses 64 bits. The int uses 32 bits, and so can only hold numbers up to ±2 billion (-2³¹ to +2³¹-1).

You should use long and int, except where you need to make use of methods inherited from Object, such as hashcode. Java.util.collections methods usually use the boxed (Object-wrapped) versions, because they need to work for any Object, and a primitive type, like int or long, is not an Object.

Another difference is that long and int are pass-by-value, whereas Long and Integer are pass-by-reference value, like all non-primitive Java types. So if it were possible to modify a Long or Integer (it's not, they're immutable without using JNI code), there would be another reason to use one over the other.

A final difference is that a Long or Integer could be null.

There are a couple of things you can't do with a primitive type:

• Have a null value
• synchronize on them
• Use them as type parameter for a generic class, and related to that:
• Pass them to an API that works with Objects

Unless you need any of those, you should prefer primitive types, since they require less memory.

• By default use an int, when holding numbers.
• If the range of int is too small, use a long
• If the range of long is too small, use BigInteger
• If you need to handle your numbers as object (for example when putting them into a Collection, handling null, ...) use Integer/Long instead