layout	title	folder	permalink	categories	tags
pattern	Promise	promise	/patterns/promise/	Concurrency	Java Functional Reactive Difficulty-Intermediate

Also known as

CompletableFuture

Intent

A Promise represents a proxy for a value not necessarily known when the promise is created. It allows you to associate dependent promises to an asynchronous action's eventual success value or failure reason. Promises are a way to write async code that still appears as though it is executing in a synchronous way.

Applicability

Promise pattern is applicable in concurrent programming when some work needs to be done asynchronously and:

• code maintainability and readability suffers due to callback hell.
• you need to compose promises and need better error handling for asynchronous tasks.
• you want to use functional style of programming.

Real world examples

• java.util.concurrent.CompletableFuture
• Guava ListenableFuture

Related Patterns

• Async Method Invocation
• Callback

Credits

• You are missing the point to Promises
• Functional style callbacks using CompletableFuture