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Promise

Difficulty-Intermediate Functional Java Reactive Concurrency

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.

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Applicability

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

  • code maintainablity 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

  • Async Method Invocation
  • Callback

Credits