CompletableFuture

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.

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.

• java.util.concurrent.CompletableFuture
• Guava ListenableFuture

• Async Method Invocation
• Callback

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