Seems to be some edge case with autocompletion. I reset everything and imported only java.time.*. Note that there is a class java.time.Instant but it has no public constructor.

This happens with JDK 15. It also happens in my development build of JDK 16, which is up-to-date within a week or so, and whose latest tag is jdk-16+16.

| Welcome to JShell -- Version 15
| For an introduction type: /help intro

jshell> /set start /dev/null

jshell> /reset
| Resetting state.

jshell> import java.time.*

jshell> new Instant // <== hit <TAB> to do completion at this point
InstantiationError( InstantiationException(

iationE
Exception in thread "main" java.lang.UnsupportedOperationException: Should not get here.
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext$ExpressionSignaturesTask.description(ConsoleIOContext.java:757)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.complete(ConsoleIOContext.java:443)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext$2.doComplete(ConsoleIOContext.java:153)
at jdk.internal.le/jdk.internal.org.jline.reader.impl.LineReaderImpl.expandOrComplete(LineReaderImpl.java:4302)
at jdk.internal.le/jdk.internal.org.jline.reader.impl.LineReaderImpl$1.apply(LineReaderImpl.java:3797)
at jdk.internal.le/jdk.internal.org.jline.reader.impl.LineReaderImpl.readLine(LineReaderImpl.java:665)
at jdk.internal.le/jdk.internal.org.jline.reader.impl.LineReaderImpl.readLine(LineReaderImpl.java:454)
at jdk.jshell/jdk.internal.jshell.tool.ConsoleIOContext.readLine(ConsoleIOContext.java:233)
at jdk.jshell/jdk.internal.jshell.tool.JShellTool.getInput(JShellTool.java:1254)
at jdk.jshell/jdk.internal.jshell.tool.JShellTool.run(JShellTool.java:1190)
at jdk.jshell/jdk.internal.jshell.tool.JShellTool.start(JShellTool.java:991)
at jdk.jshell/jdk.internal.jshell.tool.JShellToolBuilder.start(JShellToolBuilder.java:254)
at jdk.jshell/jdk.internal.jshell.tool.JShellToolProvider.main(JShellToolProvider.java:120)