Generic method throws compiler error for numeric array [duplicate]

Question

I'm attempting to call a method that returns the identity of a generic array, supplying arrays of ints and doubles as test data. My typed parameters should implement the Comparable interface, but the compiler seems to complain:

method identity in class com.me.Test cannot be applied to given types;
  required: T[]
  found:    int[]
  reason: inference variable T has incompatible bounds
    equality constraints: int
    lower bounds: java.lang.Comparable<T>

I'm new to Java, so I'm probably missing something. Any thoughts?

Code:

public class Main {

    public static void main(String[] args) {
        int[] arr1 = {1};
        double[] arr2 = {1.0};
        System.out.println(Test.identity(arr1));
        System.out.println(Test.identity(arr2));
    }
}

public class Test {
    public static <T extends Comparable<T>> T[] identity(T[] x) {
        return x;
    }
}

Generics don't work with primitive element types. You would have to use Integer[] and Double[], respectively. — Andy Turner
– Andy Turner, Commented Feb 24, 2020 at 19:20
Does this answer your question? How to use an integer array for a generic method? — kaya3
– kaya3, Commented Feb 24, 2020 at 19:40

Pedro Coelho · Accepted Answer · 2020-02-24 20:25:24Z

0

You could do something like the following (but without primitive element types, as generics do not work with them):

public class Main {

    public static <T> Class<?> identity(T[] array) {
    return array.getClass().getComponentType();
}

    public static void main(String[] args) {
        Integer[] arr1 = new Integer[]{1};
        Double[] arr2 = new Double[] {1.0};
        System.out.println(identity(arr1));
        System.out.println(identity(arr2));
    }
}

answered Feb 24, 2020 at 20:25

Pedro Coelho

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