Section 1.1: What is CompletableFuture?

CompletableFuture serves as a representation of a result that will be available in the future from an asynchronous computation. It enables developers to execute tasks asynchronously and seamlessly construct intricate asynchronous workflows. Let's explore the fundamentals of CompletableFuture through a practical example:

CompletableFuture future = CompletableFuture.supplyAsync(() -> {

// Simulate a time-consuming operation

try {

Thread.sleep(2000);

} catch (InterruptedException e) {

e.printStackTrace();

}

return "Hello";

});

future.thenApplyAsync(result -> result + " World")

.thenAccept(System.out::println)

.join(); // Wait for completion

In the above code, we generate a CompletableFuture using the supplyAsync method, which facilitates an asynchronous computation. We then link multiple asynchronous operations utilizing methods like thenApplyAsync and thenAccept.

Section 1.2: Handling Exceptions in CompletableFuture

CompletableFuture offers robust mechanisms for managing exceptions within asynchronous code. We can utilize methods such as exceptionally or handle to effectively deal with errors. Consider this example:

CompletableFuture future = CompletableFuture.supplyAsync(() -> {

// Simulate a computation that may throw an exception

if (Math.random() < 0.5) {

throw new RuntimeException("Oops! Something went wrong");

}

return 42;

});

future.exceptionally(ex -> {

System.out.println("Exception occurred: " + ex.getMessage());

return 0; // Default value in case of exception

});

Section 1.3: Combining CompletableFutures

A standout feature of CompletableFuture is the ability to merge multiple futures into one using methods such as thenCompose, thenCombine, or allOf. Here's an illustration:

CompletableFuture future1 = CompletableFuture.supplyAsync(() -> 10);

CompletableFuture future2 = CompletableFuture.supplyAsync(() -> 20);

CompletableFuture combinedFuture = future1.thenCombine(future2, Integer::sum);

combinedFuture.thenAccept(System.out::println);

In this scenario, we combine the outputs of future1 and future2 employing the thenCombine method, which accepts a BiFunction to merge the results.

Section 1.4: Managing Cancellation and Timeout

CompletableFuture also provides the capability to cancel tasks and set timeouts to prevent indefinite execution. Methods such as cancel and completeOnTimeout can be employed for this purpose. Here's how:

CompletableFuture future = CompletableFuture.supplyAsync(() -> {

// Simulate a time-consuming operation

try {

Thread.sleep(5000);

} catch (InterruptedException e) {

e.printStackTrace();

}

return "Hello";

});

future.completeOnTimeout("Timeout", 3, TimeUnit.SECONDS)

.thenAccept(System.out::println)

.join(); // Wait for completion