CompletionStage.adoc

CompletionStage

Table of Contents

• What is CompletionStage
• Classifications
  • Core methods
  • Action methods
  • Synchronicity
  • Post Execution

What is CompletionStage

Introduced in Java 8 (2014).

A java.util.concurrent.CompletionState interface represents an asynchronous or synchronous computation task.

This task performs an action or computes a value when another CompletionStage completes.

There are a few classifications that are identifiable via patterns in the method’s name.

Classifications

Core methods

Types of computation determined by method name pattern

Table 1. Core Methods

Pattern in method name	Description
apply/Apply	Function computation on result or value of the CompletionStage
accept/Accept	Consumer computation on result or value of the CompletionStage
run/Run	Runnable computation

Action methods

Actions performed determined by method name pattern

Table 2. Action methods

Pattern in method name	Description
Compose	Similar to apply, returns a new CompletionStage after the completion of the current one, thus allowing pipelines
Combine	Combine results of two completion stages into a BiFunction and returns a new CompletionStage
exceptionally	handle any exception via a Function that returns a CompletedStage, successful completion is returned as the value of CompletionStage
whenComplete	handle either successful result or exception passed as a BiConsumer and returns a new CompletionStage
handle	handle either successful result or exception passed as a BiFunction and returns a new CompletionStage

Synchronicity

Synchronicity of the stage is either Sync or Async

Table 3. Synchronicity

Pattern in method name	Description
<nothing>	synchronous
Async	asynchronous

Post Execution

Actions to perform post-execution

Table 4. Post Execution

Pattern in method name	Description
then	a single stage
Both	both of two stages
Either	either of two stages