Why am I getting an AssertionError when assigning Arrays.asList() to var directly?

Question

I'm trying to understand local variable type inference in Java 10.

The code below works perfectly during compilation and runtime:

List list1 = Arrays.asList(1L, 2.0F, "3");
var list2 = list1;

However, this line throws a compilation error:
```
var list3 = Arrays.asList(1L, 2.0F, "3");
```
Error:java: java.lang.AssertionError: Unexpected intersection type: java.lang.Object&java.io.Serializable&java.lang.Comparable<? extends java.lang.Object&java.io.Serializable&java.lang.Comparable<?>>

I don't really understand why the 2nd case is wrong but not the 1st case. Because I expect the compiler would infer the type of list1 and treat list2 and list3 the same. Thanks in advance.

I dont think that got your issue right because I tried both the statements and got executed correctly: jshell> List list3 = Arrays.asList(1L, 2.0F, "3"); list3 ==> [1, 2.0, 3] jshell> List list1 = Arrays.asList(1, 2.0, "3"); list1 ==> [1, 2.0, 3] — Aman Chhabra, Mar 29 '18 at 14:42
@AmanChhabra my point was that the OP issue is related to IntelliJ — Eugene, Mar 29 '18 at 14:45
@AmanChhabra Note the OP's code is different from what you put in your comment: `var list3` vs `List list3`. — Code-Apprentice, Mar 29 '18 at 14:51
In the first example you are using the [*raw type*](https://stackoverflow.com/q/2770321/2711488) `List`. Of course, the compiler will *not* infer the *raw type* `List` when you use `var`… — Holger, Mar 29 '18 at 17:10

ZhekaKozlov · Accepted Answer · 2018-07-18T18:14:49.647

24

This is a bug in Java 10 compiler: https://bugs.openjdk.java.net/browse/JDK-8199910

It is only reproduced when javac is called with a -g flag.

Possible workarounds:

Do not use the -g flag
- If you use IDEA: Settings → Build, Execution, Deployment → Compiler → Java Compiler → Uncheck "Generate Debugging Info"
Do not use var with intersection types (use explicit types):
- List<Object> list = Arrays.asList(1L, 2.0F, "3");
- var list = Arrays.<Object> asList(1L, 2.0F, "3");
Use Eclipse which has its own compiler

UDPATE:

The bug was fixed in JDK 10.0.2.

edited Jul 18 '18 at 18:14

answered Mar 29 '18 at 14:52

ZhekaKozlov

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thank you. it works after I uncheck "Generate Debugging Info". – hoan Mar 30 '18 at 08:38

xingbin · Answer 2 · 2018-03-29T17:17:53.067

12

This is a bug of openjdk, see this:

Javac should skip non-denotable types in the LocalVariableTypeTable attribute

edited Mar 29 '18 at 17:17

answered Mar 29 '18 at 14:53

xingbin

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I believe this will be fixed in JDK 10 too. It will be crazy if they do not backport such a critical bug. – ZhekaKozlov Mar 29 '18 at 15:19
2

Thank guys, I confirm that it works by using jshell with `java version "10" 2018-03-20 Java(TM) SE Runtime Environment 18.3 (build 10+46)` – hoan Mar 30 '18 at 08:40

Why am I getting an AssertionError when assigning Arrays.asList() to var directly?

2 Answers2

UDPATE:

Linked