Item 49: Prefer primitive types to boxed primitives

Java has a two-part type system, consisting of primitives, such as int, double, and boolean, and reference types, such as String and List. Every primitive type has a corresponding reference type, called a boxed primitive. The boxed primitives corresponding to int, double, and boolean are Integer, Double, and Boolean.

In release 1.5, autoboxing and auto-unboxing were added to the language. As mentioned in Item 5, these features blur but do not erase the distinction between the primitive and boxed primitive types. There are real differences between the two, and it’s important that you remain aware of which you are using, and that you choose carefully between them.