How to properly return generic array in Java generic method?

Question

I have below generic method that returns a generic array:

public static  T[] genericMethod1(List input) {
    T[] res = (T[]) new Object[input.s         


        

Answer 1

When calling the method, genericMethod you are assuming that it returns array of integers, which is NOT correct. It actually returns array of type Object at runtime.

    List input = new ArrayList();
    input.add(1);
    Object[] output = genericMethod(input);
    for(Object obj : output){
        System.out.println("Value= "+ (Integer)obj);
    }

So we need to cast the individual content of the array.

One general guidline is that we shouldn't mix ARRAY and GENERICS in Java.

Update:

Reference from Effective Java:

In Summary, arrays and generics have very different type rules. Arrays are covariant and reified; generics are invariant and erased. As a consequcne, arrays provide runtime type safety but not compile-time type safety and vice versa for generics. Generally speaking, arrays and generics don’t mix well. If you find yourself mixing them and getting compile-time error or warnings, your first impulse should be to replace the arrays with lists.