Catching ArrayStoreException at Compile-time

Question

Consider the following test of Java\'s ArrayList#toArray method. Note that I borrowed the code from this helpful answer.

public class GenericTest {
         


        

Answer 1

The method Collection.toArray cannot be changed for compatibility reasons.

However for your own code you can create a (more) type-safe helper method which protects you from the ArrayStoreException if you use your method consequently:

public static  T[] toArray(List list, T[] t) {
    return list.toArray(t);
}

This method will reject String[] s=toArray(new ArrayList(), new String[0]); which matches the example case of your question, but beware of the array subtyping rule: it will not reject

Object[] s=toArray(new ArrayList(), new String[0]);

because of the pre-Generics “String[] is a subclass of Object[]” rule. This can’t be solved with the existing Java language.