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

Sometimes I see API's using long or Long or int or Integer, and I can't figure how the decision is made for that?

When should I choose what?

• 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

Integer is a signed 32 bit integer type

• Denoted as Int
• Size = 32 bits (4byte)
• Can hold integers of range -2,147,483,648 to 2,147,483,647
• default value is 0

Long is a signed 64 bit integer type

• Denoted as Long
• Size = 64 bits (8byte)
• Can hold integers of range -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
• default value is 0L

If your usage of a variable falls in the 32 bit range, use Int, else use long. Usually long is used for scientific computations and stuff like that need much accuracy. (eg. value of pi).

An example of choosing one over the other is YouTube's case. They first defined video view counter as an int which was overflowed when more than 2,147,483,647 views where received to a popular video. Since an Int counter cannot store any value more than than its range, YouTube changed the counter to a 64 bit variable and now can count up to 9,223,372,036,854,775,807 views. Understand your data and choose the type which fits as 64 bit variable will take double the memory than a 32 bit variable.

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.

a) object Class "Long" versus primitive type "long". (At least in Java)

b) There are different (even unclear) memory-sizes of the primitive types:

Java - all clear: https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html

• byte, char .. 1B .. 8b
• short int .. 2B .. 16b
• int .. .. .. .. 4B .. 32b
• long int .. 8B .. 64b

C .. just mess: https://en.wikipedia.org/wiki/C_data_types

• short .. .. 16b
• int .. .. .. 16b ... wtf?!?!
• long .. .. 32b
• long long .. 64b .. mess! :-/

An int is a 32-bit integer; a long is a 64-bit integer. Which one to use depends on how large the numbers are that you expect to work with.

int and long are primitive types, while Integer and Long are objects. Primitive types are more efficient, but sometimes you need to use objects; for example, Java's collection classes can only work with objects, so if you need a list of integers you have to make it a List<Integer>, for example (you can't use int in a List directly).

When it comes to using a very long number that may exceed 32 bits to represent, you may use long to make sure that you'll not have strange behavior.

From Java 5 you can use in-boxing and out-boxing features to make the use of int and Integer completely the same. It means that you can do :

int myInt = new Integer(11);
Integer myInt2 = myInt;

The in and out boxing allow you to switch between int and Integer without any additional conversion (same for Long,Double,Short too)

You may use int all the time, but Integer contains some helper methods that can help you to do some complex operations with integers (such as Integer.parseInt(String) )