Inconsistency in java.util.concurrent.Future?

For the sake of argument, let's say I'm implementing Future for a task which is not cancelable. The Java 6 API doc says:

After [cancel()] returns, subsequent calls to isDone() will always return true.

[cancel()] returns false if the task could not be cancelled, typically because it has already completed normally

It also says:

[isDone()] returns true if this task completed.

But what if my cancellation fails not because the task is already complete开发者_JS百科d, but because it simply cannot be cancelled? Is there a way out of this contradiction (other than making my uncancelable task cancelable and sidestepping it altogether)?

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It does seem like the doc should say

After cancel() returns true, subsequent calls to isDone()...

The Javadocs are often flat-out wrong and contradictory, and Sun has often not even bothered to fix them even after 10 years. Careful testing should always supplement the docs.