您可以将原始类型用于类或方法中的泛型参数吗？

Question

I am writing a short paper on generics and I have not really used them all that much in Java. I was wondering if a primitive type can be used as a parameter type in a generic variable. I have not been able to get it to compile with a generic parameter that is of a generic type.

Question: I am somewhat not certain as to how generics can handle primitive datatypes. Can someone example how I would have to declare the method different to not have to add a cast to the int type with Integer and if it is possible to use a primitive Java datatype in the class declaration

   DDHGeneric<int,int,int,int> t = new DDHGeneric<int,int,int,int>();

Is there a way to do this?

The following declaration does not compile either. I do know that from what I know about generics that there is a different between using the primitive data types and a user-defined class.

   DDHGeneric<int, int, int, int> temp2 = new  DDHGeneric<int, int, int, int>();

Class:

public class DDHGeneric<T,K,Bigfoot,Pizza> {
    T a;
    K n;
    Bigfoot u;

    public DDHGeneric() {
    }

    private <rapper> void myMethod(rapper y) {
    int temp = y; <--Errors out on this line as will.
}

    public <Pizza> void myAddition(Pizza a, Pizza b) {
    }

    private <K> void me(K a, K b, K c) {
    }

    public static void main(String[] args) {
         DDHGeneric<int, Integer, Integer, Integer> temp = new  DDHGeneric<int, Integer, Integer, Integer>();
         temp.myAddition(5, 4);
         temp.a = "Test this string!" ;
    }
}

Answer 1

You cannot.

Oracle gives an article on this topic .

to quote:

When creating a Pair object, you cannot substitute a primitive type for the type parameter K or V:

Pair<int, char> p = new Pair<>(8, 'a'); // compile-time error

You can substitute only non-primitive types for the type parameters K and V:

Pair<Integer, Character> p = new Pair<>(8, 'a');

Answer 2

No.

Generics aren't meant to represent primitives. They're meant to represent objects (as the generic types all extend Object implicitly ).

You can use the wrapper variants of the primitive class you want instead to achieve the same effect.

 DDHGeneric<Integer, Integer, Integer, Integer> t = new DDHGeneric<>();

Here is a brief excerpt from Why Use Generics? , found in the Java Trails:

In a nutshell, generics enable types (classes and interfaces) to be parameters when defining classes, interfaces and methods.

Answer 3

Generics only take primitive class but not the primitive data type.

For each data type used its corrasponding class for it

DDHGeneric<int,int,int,int> t = new DDHGeneric<int,int,int,int>();

can be used as

DDHGeneric<Integer, Integer, Integer, Integer> t = new DDHGeneric<Integer, Integer, Integer, Integer>();