Illustration of exceptionally method of CompletableFuture

ExceptionallyExample.java

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

public class ExceptionallyExample {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        int val = 0;
        CompletableFuture<String> completableFuture = CompletableFuture.supplyAsync(() -> {
            if(val == 0) {
                throw new IllegalArgumentException("Value is 0");
            }
            if(val > 0) {
                return "Positive value!";
            } else {
                return "Negative value!";
            }
        }).exceptionally(ex -> { // printing error messages & returning a default value
            System.out.println("Failed due: " + ex.getMessage());
            return "Default value!";
        });
        //get() blocks and gets the result of the Future
        System.out.println(completableFuture.get());
    }
}

/***************************************************************************
 * Output:
 * Failed due: java.lang.IllegalArgumentException: Value is 0
 * Default value!
 **************************************************************************/