原始类和原始数据类型之间有什么区别？

Question

I am reading a book on Java, and they seem to use the two terms "primitive class" and "primitive data type" interchangeably.

What's the difference between the two? I understand that Integer is a wrapper class, and people reference int as a primitive data type. So is it also a primitive class?

Answer 1

They're confusing their vernacular here.

A primitive is a data type which is not an object. int , float , double , long , short , boolean and char are examples of primitive data types. You can't invoke methods on these data types and they don't have a high memory footprint, which is their striking difference from classes.

Everything else is a class (or class-like in the case of interfaces and enums). Pretty much everything that begins with an upper-case letter, like String , Integer are classes. Arrays also classify as not-primitives, even though they may hold them. int[] isn't a primitive type but it holds primitives.

The only thing that could realistically come close would be the wrapper classes, as explained by the JLS , but even then, they're still classes, and not primitives.

Answer 2

Primitive class has a special meaning in the context of reflection APIs: when you need to retrieve a method that takes a parameter of primitive type, you need a primitive class object that corresponds to that primitive type.

This is important if you must distinguish between overloads that take primitives and overloads that take wrappers:

void someMethod(int n);
void someMethod(Integer n);

There are two ways to obtain this class object:

• Using class literal, eg int.class , or
• Using TYPE member of the corresponding wrapper class, eg Integer.TYPE .

This is not the same class as the class representing the primitive wrapper. In other words,

int.class != Integer.class