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

tonyhoan :

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

1. The code below works perfectly during compilation and runtime:

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

2. 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.

ZhekaKozlov :

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:

1. Do not use the -g flag
   • If you use IDEA: Settings → Build, Execution, Deployment → Compiler → Java Compiler → Uncheck "Generate Debugging Info"
2. 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");
3. Use Eclipse which has its own compiler

UDPATE:

The bug was fixed in JDK 10.0.2.

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