Generic unmodifiableList

Question

I wrote:

this.array = (X[]) Array.newInstance(init.getClass(), size);

// ...

public List<X> get()  {        
    return Collections.<X>unmodifiableList(this.array);
}

But I get the error:

unmodifiableList in Collections cannot be applied to (X[])

How can I create a generic unmodifiable list?

@shmosel as I read again the comment I've written, it seems quite wrong to me, as OP probably has a populated array and not an empty one. But if he does want to return an empty list your approach is better — Lino, Jul 27 '17 at 09:34

score 2 · Answer 1 · answered Jul 27 '17 at 08:38

2

You need to do it like this:

public List<X> get()
{
    List<X> modifiableList = Arrays.asList( this.array );
    return Collections.unmodifiableList( modifiableList );
}

answered Jul 27 '17 at 08:38

Mike Nakis

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alaster · Answer 2 · 2017-07-27T09:14:43.467

1

You can do this:

public List<X> get()  {
    return Collections.unmodifiableList(Arrays.asList(this.array));
}

edited Jul 27 '17 at 09:14

answered Jul 27 '17 at 08:33

alaster

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The first option won't work as there is no ArrayList constructor that accepts array. The second one though is correct – Michael Gantman Jul 27 '17 at 09:06
Cool, it is now fully correct answer even though it makes it identical to a second answer. – Michael Gantman Jul 27 '17 at 09:22

Generic unmodifiableList

2 Answers2