Why do I need to cast the result of myCollection.toArray(new String[0])

Asked Aug 20 '18 at 14:40

Active Aug 20 '18 at 14:40

Viewed 37 times

The Collection#toArray(T[]) signature is the following

public <T> T[] toArray(T[] a)

Most of the time, I write this code and everything works :

Collection<String> myCollection = Arrays.asList("foo", "bar");
String[] myArray = myCollection.toArray(new String[0]);

Today, I can't get my "usual" Collection<String> for some reasons, and then I came up with :

Collection myCollection = someNonGenericResult();
String[] myArray = myCollection.toArray(new String[0]);

And in this case, I get this compilation error :

incompatible types: java.lang.Object[] cannot be converted to java.lang.String[]

I know that I can cast the result of myCollection.toArray(new String[0]), but I would like to know why. I believed the method genericity could avoid that.

asked Aug 20 '18 at 14:40

yunandtidus

3,847
3
29
42

because a generic Collection might not include only strings. – Hongyu Wang Aug 20 '18 at 14:44
2

[See the section titled *A raw type is the erasure of that type*.](https://stackoverflow.com/a/2770692/2891664) – Radiodef Aug 20 '18 at 14:48
the SO community is really impressive ... – yunandtidus Aug 20 '18 at 15:23

Why do I need to cast the result of myCollection.toArray(new String[0])

0 Answers0