Method reference to array clone() causes NoClassDefFoundError: Array

Question

When I run this code

List<int[]> list = Arrays.asList(new int[]{1, 2, 3}, new int[]{4, 5});
int[][] arr = list.stream().map(j -> j.clone()).toArray(int[][]::new);
System.out.println(Arrays.deepToString(arr));

it works as expected and I get the output

[[1, 2, 3], [4, 5]]

However, if I replace the lambda by a method reference for clone()

int[][] arr = list.stream().map(int[]::clone).toArray(int[][]::new);

I get a runtime exception:

Exception in thread "main" java.lang.NoClassDefFoundError: Array
    at Main.lambda$MR$main$clone$8ed4b78b$1(Main.java:14)
    at Main$$Lambda$1/1160460865.apply(Unknown Source)
    at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
    at java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
    at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502)
    at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:576)
    at java.util.stream.AbstractPipeline.evaluateToArrayNode(AbstractPipeline.java:255)
    at java.util.stream.ReferencePipeline.toArray(ReferencePipeline.java:438)
    at Main.main(Main.java:14)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)
Caused by: java.lang.ClassNotFoundException: Array
    at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)

I don't understand this at all. I would have thought the method reference and the lambda were equivalent. Also it seems a really strange exception to get. Can anyone explain?

I am using JDK 1.8.0_25.

Answer 1

This is bug JDK-8056051. It's listed as fixed in 8u40.

Based on the bug comments, javac uses a dummy Array class at some point during compilation and forgets to rewrite it to the actual array class, causing this error.