How to make a Java Generic method static?

java generics
Chris Johnson picture Chris Johnson · Dec 10, 2010 · Viewed 163.5k times · Source

The following is a snippet on how to make a java generic class to append a single item to an array. How can I make appendToArray a static method. Adding static to the method signature results in compile errors.

public class ArrayUtils<E> {

        public E[] appendToArray(E[] array, E item) {
            E[] result = (E[])new Object[array.length+1];
            result[array.length] = item;
            return result;
        }
}

Answer

scheffield picture scheffield · Dec 10, 2010

the only thing you can do is to change your signature to

public static <E> E[] appendToArray(E[] array, E item)

Important details:

Generic expressions preceding the return value always introduce (declare) a new generic type variable.

Additionally, type variables between types (ArrayUtils) and static methods (appendToArray) never interfere with each other.

So, what does this mean: In my answer <E> would hide the E from ArrayUtils<E> if the method wouldn't be static. AND <E> has nothing to do with the E from ArrayUtils<E>.

To reflect this fact better, a more correct answer would be:

public static <I> I[] appendToArray(I[] array, I item)

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