CODEWITHSUNDEEP
javagenerics
Global Warrior
Global Warrior

Reputation: 5110

getting .class for List <int> in java

I have the following function

EDIT: Changed int to class Long

protected <T> ApiResponse<T> getApiResponse(Object obj, Class<T> clasx)

How can I pass List<Long> class as the second argument?

Can I pass List<Long>.class but that is not working?

Upvotes: 2

Views: 3167

Answers (2)

user1373996
user1373996

Reputation:

You cannot pass int into the List. Because the T here should be extends from Object.

Integer is extended from Object, but not int.

Upvotes: 0

Greg Kopff
Greg Kopff

Reputation: 16545

Type erasure means that you can only pass List.class.

From the linked documentation:

When a generic type is instantiated, the compiler translates those types by a technique called type erasure — a process where the compiler removes all information related to type parameters and type arguments within a class or method. Type erasure enables Java applications that use generics to maintain binary compatibility with Java libraries and applications that were created before generics.

For instance, Box<String> is translated to type Box, which is called the raw type — a raw type is a generic class or interface name without any type arguments. This means that you can't find out what type of Object a generic class is using at runtime. The following operations are not possible:

public class MyClass<E> {
  public static void myMethod(Object item) {
    // Compiler error
    if (item instanceof E) {
        ...
    }
    E item2 = new E();       // Compiler error
    E[] iArray = new E[10];  // Compiler error
    E obj = (E)new Object(); // Unchecked cast warning
  }
}

The operations shown in bold are meaningless at runtime because the compiler removes all information about the actual type argument (represented by the type parameter E) at compile time.

Upvotes: 8

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