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null type mismatch with eclipse 4.4rc1 and java 1.8 [message #1378575]

Sat, 24 May 2014 09:38

Nicola Zanaga

Messages: 56
Registered: July 2009

Member

using eclipse 4.4RC1 with "compiler compliance level 1.7", the code below is fine, but with "compiler compliance level 1.8", it doesn't work.

if you use "(E)null" instead of "null" the code work with a warning

import org.eclipse.jdt.annotation.Nullable;

public class Test2<E> {

@Nullable
E test() {
return null;
}

void test2() {
E local = null;
}

}

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Re: null type mismatch with eclipse 4.4rc1 and java 1.8 [message #1379023 is a reply to message #1378575]

Sat, 24 May 2014 14:11

Thomas Schindl

Messages: 6651
Registered: July 2009

Senior Member

That's to be expected! You need to annotate the generic type

> import org.eclipse.jdt.annotation.Nullable;
>
> public class Test2<@Nullable E> {
> @Nullable
> E test() {
> return null;
> }
>
> void test2() {
> E local = null;
> }
> }

I had the same missunderstanding see
https://bugs.eclipse.org/bugs/show_bug.cgi?id=434374#c8 and
https://bugs.eclipse.org/bugs/show_bug.cgi?id=434374#c11

Tom

On 24.05.14 11:38, Nicola Zanaga wrote:
> import org.eclipse.jdt.annotation.Nullable;
>
> public class Test2<E> {
> @Nullable
> E test() {
> return null;
> }
> void test2() {
> E local = null;
> }
> }

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Re: null type mismatch with eclipse 4.4rc1 and java 1.8 [message #1379174 is a reply to message #1379023]

Sat, 24 May 2014 15:43

Nicola Zanaga

Messages: 56
Registered: July 2009

Member

I have read the bugs, but I don't understand why it is related.
I declared the variable @Nullable, so it has to be nullable, indeed (E)null works ok.

the declaration
public class Test2<@Nullable E> {
}
give me an error, maybe I miss something

However, E type can be null or not null at class level, but I think I always can do a local variable null:

@NonNull E test2() {
E local = null;
...
if( local != null )
return E;
....
}

Thomas Schindl wrote on Sat, 24 May 2014 10:11

That's to be expected! You need to annotate the generic type

> import org.eclipse.jdt.annotation.Nullable;
>
> public class Test2<@Nullable E> {
> @Nullable
> E test() {
> return null;
> }
>
> void test2() {
> E local = null;
> }
> }

I had the same missunderstanding see
https://bugs.eclipse.org/bugs/show_bug.cgi?id=434374#c8 and
https://bugs.eclipse.org/bugs/show_bug.cgi?id=434374#c11

Tom

On 24.05.14 11:38, Nicola Zanaga wrote:
> import org.eclipse.jdt.annotation.Nullable;
>
> public class Test2<E> {
> @Nullable
> E test() {
> return null;
> }
> void test2() {
> E local = null;
> }
> }

Report message to a moderator

Re: null type mismatch with eclipse 4.4rc1 and java 1.8 [message #1379412 is a reply to message #1379174]

Sat, 24 May 2014 18:08

Stephan Herrmann

Messages: 1853
Registered: July 2009

Senior Member

The semantics of null type annotations in relation to type parameters and type variables still needs to be documented. I hope I'll find the time to include the basic explanations into the Luna migration guide.

Basically, all examples you give work as designed, but:

Quote: