Why doesn't Arrays.toList work?

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Chris Smowton - 10 Jul 2006 12:10 GMT

I've seen a few things on the internet say that if you want a list from
an array, you should go

int[] test = {1, 2, 3, 4, 5};

List myList = Arrays.toList(test);

However, on Java 5 this doesn't seem to work, it tries to produce a
List<Integer[]> instead of a List<Integer>.

Obviously I could fix this by calling toList(1, 2, 3, 4, 5), but this
is hardly practical when a function returns a long array.

For the record, the specific application is I want an ArrayList of the
UTF-8 bytes of some string.

Thanks if anyone can help,

Chris

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Thomas Hawtin - 10 Jul 2006 12:39 GMT

> I've seen a few things on the internet say that if you want a list from
> an array, you should go
[quoted text clipped - 5 lines]
> However, on Java 5 this doesn't seem to work, it tries to produce a
> List<Integer[]> instead of a List<Integer>.

List<int[]>. int[] isn't assignment compatible to Object[], therefore
the line is treated as:

List myList = Arrays.<int[]>asList(new int[][] { test });

> Obviously I could fix this by calling toList(1, 2, 3, 4, 5), but this
> is hardly practical when a function returns a long array.

If you want to use asList, you will need to box the primitive individually:

final int num = test.length;
final Integer[] boxed = new Integer[num];
for (int ct=0; ct<num; ++ct) {
boxed[ct] = test[ct];
}
final List<Integer> myList = Arrays.asList(boxed);

Alternative write, or acquire, an implementation of List that backs to
an int[] (and boxes/unboxes) instead of a reference array.

> For the record, the specific application is I want an ArrayList of the
> UTF-8 bytes of some string.

So shouldn't that be List<Byte>? Arrays.asList actually returns a
(package? private) java.util.Arrays.ArrayList not a java.util.ArrayList.

Tom Hawtin

Signature

Unemployed English Java programmer
http://jroller.com/page/tackline/

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Chris Smowton - 10 Jul 2006 12:47 GMT

Indeed, I am using <Byte>, that was just a quickly scrawled example.

Thanks for your reply; I thought it might be something along those
lines, it just struck me as odd you couldn't just go

ArrayList<Byte> utf8bytes = new
ArrayList<Byte>(myString.getBytes("UTF-8"));

since Java is usually so heavy on convenience methods.

Apparently nobody at Sun thought that might be handy...

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Red Orchid - 11 Jul 2006 07:47 GMT

"Chris Smowton" <chris@smowton.net> wrote or quoted in
Message-ID: <1152532064.789695.220220@m73g2000cwd.googlegroups.com>:

> ArrayList<Byte> utf8bytes = new
> ArrayList<Byte>(myString.getBytes("UTF-8"));

If it is possible not to use 'List', it will be more better to
use the following.

- Trove collections (http://trove4j.sourceforge.net/)
or
- ByteBuffer, IntBuffer (java.nio.*)
or
- Your implementation of primitive list.

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Dave Glasser - 10 Jul 2006 16:39 GMT

Thomas Hawtin <usenet@tackline.plus.com> wrote on Mon, 10 Jul 2006
12:42:58 +0100 in comp.lang.java.programmer:

>Tom Hawtin

Are things really that bad in southern England, that a decent Java
programmer will have a hard time finding work? I'm not implying
anything by asking, it just seems that the economy there would have to
be pretty dismal for that to be the case.

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Thomas Hawtin - 10 Jul 2006 19:43 GMT

> Thomas Hawtin <usenet@tackline.plus.com> wrote on Mon, 10 Jul 2006
> 12:42:58 +0100 in comp.lang.java.programmer:
[quoted text clipped - 5 lines]
> anything by asking, it just seems that the economy there would have to
> be pretty dismal for that to be the case.

I think it's more a case of managers wanting to copy the decisions of
others rather than making any themselves.

Tom Hawtin

Signature

Unemployed English Java programmer
http://jroller.com/page/tackline/

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Dave Glasser - 10 Jul 2006 20:28 GMT

Thomas Hawtin <usenet@tackline.plus.com> wrote on Mon, 10 Jul 2006
19:47:32 +0100 in comp.lang.java.programmer:

>> Thomas Hawtin <usenet@tackline.plus.com> wrote on Mon, 10 Jul 2006
>> 12:42:58 +0100 in comp.lang.java.programmer:
[quoted text clipped - 8 lines]
>I think it's more a case of managers wanting to copy the decisions of
>others rather than making any themselves.

Uh, thanks, but I'm not following what you said.

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Why doesn't Arrays.toList work?

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