Java™ How To Program (Early Objects), Tenth Edition

Performing Fibonacci Calculations Asynchronously

Lines 38–41 in main launch the asynchronous Fibonacci calculations in separate threads. CompletableFuture static method supplyAsync executes an asynchronous task that returns a value. The method receives as its argument an object that implements interface Sup- plier—in this case, we use a lambdas with empty parameter lists to invoke startFibonacci(45) (line 39) and startFibonacci(44) (line 41). The compiler infers that supplyAsync returns a CompletableFuture<TimeData> because method startFibonacci returns type TimeData. Class CompletableFuture also provides static method runAsync to execute an asynchronous task that does not return a result—this method receives a Runnable.