demoThenCombine.java

private static void demoThenCombine() throws InterruptedException, ExecutionException {
        long timeStampStart = System.currentTimeMillis();
        CompletableFuture<String> completableFutureFirst = CompletableFuture.supplyAsync(() -> {
            System.out.println("Task Running inside completable Future");
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            return "one plus ";
        });

        CompletableFuture<String> completableFutureSecond = CompletableFuture.supplyAsync(() -> {
            System.out.println("Task Running inside completable Future");
            return "two";
        });

        CompletableFuture<String> completableFutureThird = completableFutureFirst.thenCombine(completableFutureSecond, (resultOne, resultTwo) -> {
            return (resultOne + resultTwo + " is three");
        });

        String result = completableFutureThird.get();
        long timeStampEnd = System.currentTimeMillis();
        System.out.println("Time taken in the Completable Future operation is " + (timeStampEnd - timeStampStart));
        System.out.println("Result is :: "+result);
    }