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8361972: Clarify the condition of System.console() about standard input/output #26299

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8361972: Clarify the condition of System.console() about standard input/output #26299

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naotoj Jul 14, 2025
e2a64c9
Wording modification
naotoj Jul 14, 2025
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Merge branch 'master' into JDK-8361972-System-console-condition
naotoj Jul 22, 2025
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Wording change, isTerminal() always returns true
naotoj Jul 22, 2025
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6 changes: 4 additions & 2 deletions src/java.base/share/classes/java/io/Console.java
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Expand Up @@ -45,8 +45,10 @@
* output streams then its console will exist and will typically be
* connected to the keyboard and display from which the virtual machine
* was launched. If the virtual machine is started automatically, for
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@justin-curtis-lu justin-curtis-lu Jul 14, 2025 •
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I think it might read easier if we reword the structure of the sentence to make it more concise.

E.g.

The virtual machine may not have a console if started automatically, (e.g., by a background scheduler) or if either the standard input or output has been redirected.

* example by a background job scheduler, then it may not
* have a console.
* example by a background job scheduler, then it may not have a
* console. Regardless of how the virtual machine was created, it may not
* have a console if either the standard input or output stream is
* redirected.
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Can you clarify what the intent of "it may not have a console" is? Initially I though the intention was that there is no Console when either stdout or stdin is redirected. However, the sentence suggests there may or may not be a Console.

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I was considering the case for jshell, where its System.console() returns a Console instance regardless of the isTTY state:

jdk/src/jdk.jshell/share/classes/jdk/jshell/execution/impl/ConsoleImpl.java

Line 70 in bd55d7a

return console = new RemoteConsole(remoteOutput, remoteInput);

That led me to use may in the updated spec. I'd appreciate your suggestions on wording.

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Since the decision of whether a console exists is dependent on the implementation as specified,

Whether a virtual machine has a console is dependent upon the underlying platform

And the existing wording in this paragraph uses open-ended words such as "may" and "typically", it makes sense to me that this change would follow the same style of wording. If you wanted to concretely define what this implementation does, using one of the @impl tags to describe the behavior could be an option?

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Okay, so the intent is to specify that it is implementation or configuration specific as to whether there is a Console when standard input or output, but not both, are redirected, is that right? What should users expect isTerminal to return in this case?

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For the jshell case, I think it can return true from its isTerminal() as it is infact interactive environment. That means all the Console implementations return true so that we can replace that "may not have a Console" with "will not have a Console", which is clearer.

* <p>
* If this virtual machine has a console then it is represented by a
* unique instance of this class which can be obtained by invoking the
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