Guide to CompletionException in Java

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Overview

The CompletionException extends from the RuntimeException and is thrown when a task hits an error or exception when executing.

The CompletionException and the ExecutionException might seem similar but there’s a fundamental difference between the two. The ExecutionException is thrown only when an attempt is made to retrieve the result/outcome of a task, while the CompletionException can be thrown when waiting on a task to complete or when trying to retrieve a result computed by a task. In a sense CompletionException can be thought of as broader in scope than ExecutionException.

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