demoCancel.java

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

        completableFutureFirst.cancel(true);

        boolean isCancelled = completableFutureFirst.isCancelled();
        System.out.println("Completable Future is cancelled :: "+isCancelled);

        String result = completableFutureFirst.get();

        System.out.println("Result :: "+result);
    }