Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/9358#discussion_r43840774
--- Diff: sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala ---
@@ -441,6 +537,17 @@ class Dataset[T] private(
/** Collects the elements to an Array. */
def collect(): Array[T] = rdd.collect()
+ /**
+ * (Java-specific)
+ * Collects the elements to a Java list.
+ *
+ * Due to the incompatibility problem between Scala and Java, the return
type of [[collect()]] at
--- End diff --
Will the class tag do the trick? I tried to define a generic class with
ClassTag:
```
class MyTest[T : ClassTag] {
def t(): Array[T] = null
}
object MyTest {
def apply[T](cls: Class[T]): MyTest[T] = {
new MyTest[T]()(ClassTag(cls))
}
}
```
The return type of `MyClass.t()` is still `Object` at java side.
I also tried to use scala RDD at java side, the return type of
`RDD.collect()` is also `Object`.
One possible solution is to define `T <: AnyRef`, but I think it's hard to
make it for `Dataset` or `RDD`.
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at [email protected] or file a JIRA ticket
with INFRA.
---
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
