Hello,
When doing refactorings to take advantage of newer Java features, I hit a
new and weird edge case. I trimmed down the code several times, and ended
up with the following tiny reproducer, and I don't understand what javac is
complaining about even with javac 24:
(Note: unlike the original code, this reproducer is very contrived, so
there's no need to make comments on how bad it is: I fully agree)
```java
1 import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
public class Main {
private static final class Child<T> {
public List<String> getValues() {
return new ArrayList<>();
}
}
@SuppressWarnings("unchecked")
private static String getString1(Child c) {
// Compilation error:
// Main.java:16: error: incompatible types: Object cannot be
converted to String
return c.getValues().stream().collect(Collectors.joining());
}
private static String getString2(Child c) {
// Compilation error:
// Main.java:27: warning: [unchecked] unchecked conversion
// List<String> values = c.getValues();
// ^
// required: List<String>
// found: List
//1 warning
List<String> values = c.getValues();
return values.stream().collect(Collectors.joining());
}
}
```
It turns out IntelliJ is a bit more eloquent than javac, and when hovering
over the warning on `c.getValues()` at the line with `List<String> values =
c.getValues();`, it reports the following:
> Unchecked assignment: 'java.util.List' to
'java.util.List<java.lang.String>'. Reason: 'c' has raw type, so result of
getValues is erased
Is it possible that javac is doing early type erasure when analysing this
code, erasing a bit too much? Even if the code uses `Child` without type
argument, I would expect the return type of `getValues()` to be well
defined as `List<String>`?
What do you think?
I am sure there is some rational explanation that I missed for this
behaviour. I could not find a JBS issue showing the same case as here.
Thank you,
Jean-Noël Rouvignac
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