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https://issues.apache.org/jira/browse/FLINK-3444?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15260115#comment-15260115
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Till Rohrmann commented on FLINK-3444:
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I'm wondering why the above described problem was solved by introducing an
overloaded method {{fromElements}} which takes as the first parameter the
{{Class<T>}} of the elements? The problem is that if you do something like
{{env.fromElements(SubClass.class, new ParentClass())}} then the vararg only
variant of {{fromElements}} will be called with type {{Object}} as result
(since Object is the super type of {{Class<SubClass>}} and {{ParentClass}}. The
reason is that {{ParentClass}} is not a subtype of {{SubClass}} and thus the
new {{fromElements}} method is not applicable.
Wouldn't it have been better to automatically infer the super type of all given
elements? Usually the {{fromElements}} method is only called for very few
elements and, thus, it should be feasible to iterate over all elements to
extract the common super type.
> env.fromElements relies on the first input element for determining the
> DataSet/DataStream type
> ----------------------------------------------------------------------------------------------
>
> Key: FLINK-3444
> URL: https://issues.apache.org/jira/browse/FLINK-3444
> Project: Flink
> Issue Type: Bug
> Components: DataSet API, DataStream API
> Affects Versions: 0.10.0, 1.0.0
> Reporter: Vasia Kalavri
> Fix For: 1.1.0
>
>
> The {{fromElements}} method of the {{ExecutionEnvironment}} and
> {{StreamExecutionEnvironment}} determines the DataSet/DataStream type by
> extracting the type of the first input element.
> This is problematic if the first element is a subtype of another element in
> the collection.
> For example, the following
> {code}
> DataStream<Event> input = env.fromElements(new Event(1, "a"), new SubEvent(2,
> "b"));
> {code}
> succeeds, while the following
> {code}
> DataStream<Event> input = env.fromElements(new SubEvent(1, "a"), new Event(2,
> "b"));
> {code}
> fails with "java.lang.IllegalArgumentException: The elements in the
> collection are not all subclasses of SubEvent".
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