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https://issues.apache.org/jira/browse/FLINK-5319?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15804274#comment-15804274
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Timo Walther commented on FLINK-5319:
-------------------------------------
Would this change break binary backwards compatibility? I'm not sure if the
community would accept this change only because of a Java bug that might be
solved in future releases.
> ClassCastException when reusing an inherited method reference as KeySelector
> for different classes
> --------------------------------------------------------------------------------------------------
>
> Key: FLINK-5319
> URL: https://issues.apache.org/jira/browse/FLINK-5319
> Project: Flink
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.2.0
> Reporter: Alexander Chermenin
> Assignee: Timo Walther
>
> Code sample:
> {code}static abstract class A {
> int id;
> A(int id) {this.id = id; }
> int getId() { return id; }
> }
> static class B extends A { B(int id) { super(id % 3); } }
> static class C extends A { C(int id) { super(id % 2); } }
> private static B b(int id) { return new B(id); }
> private static C c(int id) { return new C(id); }
> /**
> * Main method.
> */
> public static void main(String[] args) throws Exception {
> StreamExecutionEnvironment environment =
> StreamExecutionEnvironment.getExecutionEnvironment();
> B[] bs = IntStream.range(0, 10).mapToObj(Test::b).toArray(B[]::new);
> C[] cs = IntStream.range(0, 10).mapToObj(Test::c).toArray(C[]::new);
> DataStreamSource<B> bStream = environment.fromElements(bs);
> DataStreamSource<C> cStream = environment.fromElements(cs);
> bStream.keyBy((KeySelector<B, Integer>) A::getId).print();
> cStream.keyBy((KeySelector<C, Integer>) A::getId).print();
> environment.execute();
> }
> {code}
> This code throws next exception:
> {code}Exception in thread "main"
> org.apache.flink.runtime.client.JobExecutionException: Job execution failed.
> at
> org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$7.apply$mcV$sp(JobManager.scala:901)
> at
> org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$7.apply(JobManager.scala:844)
> at
> org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$7.apply(JobManager.scala:844)
> at
> scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
> at
> scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
> at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:41)
> at
> akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:401)
> at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
> at
> scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.pollAndExecAll(ForkJoinPool.java:1253)
> at
> scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1346)
> at
> scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
> at
> scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
> Caused by: java.lang.RuntimeException: Could not extract key from
> org.sample.flink.examples.Test$C@5e1a8111
> at
> org.apache.flink.streaming.runtime.io.RecordWriterOutput.collect(RecordWriterOutput.java:75)
> at
> org.apache.flink.streaming.runtime.io.RecordWriterOutput.collect(RecordWriterOutput.java:39)
> at
> org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:746)
> at
> org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:724)
> at
> org.apache.flink.streaming.api.operators.StreamSourceContexts$NonTimestampContext.collect(StreamSourceContexts.java:84)
> at
> org.apache.flink.streaming.api.functions.source.FromElementsFunction.run(FromElementsFunction.java:127)
> at
> org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:75)
> at
> org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:56)
> at
> org.apache.flink.streaming.runtime.tasks.SourceStreamTask.run(SourceStreamTask.java:56)
> at
> org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:269)
> at org.apache.flink.runtime.taskmanager.Task.run(Task.java:655)
> at java.lang.Thread.run(Thread.java:745)
> Caused by: java.lang.RuntimeException: Could not extract key from
> org.sample.flink.examples.Test$C@5e1a8111
> at
> org.apache.flink.streaming.runtime.partitioner.KeyGroupStreamPartitioner.selectChannels(KeyGroupStreamPartitioner.java:61)
> at
> org.apache.flink.streaming.runtime.partitioner.KeyGroupStreamPartitioner.selectChannels(KeyGroupStreamPartitioner.java:32)
> at
> org.apache.flink.runtime.io.network.api.writer.RecordWriter.emit(RecordWriter.java:83)
> at
> org.apache.flink.streaming.runtime.io.StreamRecordWriter.emit(StreamRecordWriter.java:86)
> at
> org.apache.flink.streaming.runtime.io.RecordWriterOutput.collect(RecordWriterOutput.java:72)
> ... 11 more
> Caused by: java.lang.ClassCastException: org.sample.flink.examples.Test$C
> cannot be cast to org.sample.flink.examples.Test$B
> at
> org.apache.flink.streaming.runtime.partitioner.KeyGroupStreamPartitioner.selectChannels(KeyGroupStreamPartitioner.java:59)
> ... 15 more{code}
> This problem occurs when we use method reference as KeySelector. And there
> are no problems when we use anonymous class or lambda.
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