FULL PRODUCT VERSION :
java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601]

A DESCRIPTION OF THE PROBLEM :
Using Stream API to put a lot of records in HashMap cause ClassCastException. This is probably based on the new structure of HashMap with TreeNodes. In test method used 200 thousands put calls.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1) Create HashMap instance.
2) Using Parallel Stream to insert ~200,000 records in this instance.
3) If Exception does not occur repeat step 1-2.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Not thread safe put in map. Possible wrong map size param and count of map entries.
Without Exception.
ACTUAL -
Throws of java.lang.ClassCastException: java.util.HashMap$Node cannot be cast to java.util.HashMap$TreeNode

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "main" java.lang.ClassCastException
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at java.util.concurrent.ForkJoinTask.getThrowableException(Unknown Source)
at java.util.concurrent.ForkJoinTask.reportException(Unknown Source)
at java.util.concurrent.ForkJoinTask.invoke(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp.evaluateParallel(Unknown Source)
at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateParallel(Unknown Source)
at java.util.stream.AbstractPipeline.evaluate(Unknown Source)
at java.util.stream.ReferencePipeline.forEach(Unknown Source)
at concurrent.cache.Bug.main(Bug.java:14)
Caused by: java.lang.ClassCastException: java.util.HashMap$Node cannot be cast to java.util.HashMap$TreeNode
at java.util.HashMap$TreeNode.moveRootToFront(Unknown Source)
at java.util.HashMap$TreeNode.treeify(Unknown Source)
at java.util.HashMap.treeifyBin(Unknown Source)
at java.util.HashMap.putVal(Unknown Source)
at java.util.HashMap.put(Unknown Source)
at concurrent.cache.Bug.lambda$1(Bug.java:14)
at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(Unknown Source)
at java.util.stream.IntPipeline$4$1.accept(Unknown Source)
at java.util.Spliterators$IntArraySpliterator.forEachRemaining(Unknown Source)
at java.util.Spliterator$OfInt.forEachRemaining(Unknown Source)
at java.util.stream.AbstractPipeline.copyInto(Unknown Source)
at java.util.stream.ForEachOps$ForEachTask.compute(Unknown Source)
at java.util.concurrent.CountedCompleter.exec(Unknown Source)
at java.util.concurrent.ForkJoinTask.doExec(Unknown Source)
at java.util.concurrent.ForkJoinPool$WorkQueue.execLocalTasks(Unknown Source)
at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(Unknown Source)
at java.util.concurrent.ForkJoinPool.runWorker(Unknown Source)
at java.util.concurrent.ForkJoinWorkerThread.run(Unknown Source)


REPRODUCIBILITY :
This bug can be reproduced rarely.

---------- BEGIN SOURCE ----------
Map<String, String> map = new HashMap<>();
IntStream.iterate(1, i -> i + 1).limit(200_000).mapToObj(String::valueOf).parallel()
    .forEach((k) -> map.put(k, "String" + k));

---------- END SOURCE ----------