// concurrent/CompletableExceptions.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
import java.util.concurrent.*;

public class CompletableExceptions {
 static CompletableFuture<Breakable>
 test(String id, int failcount) {
 return
 CompletableFuture.completedFuture(
 new Breakable(id, failcount))
 .thenApply(Breakable::work)
 .thenApply(Breakable::work)
 .thenApply(Breakable::work)
 .thenApply(Breakable::work);
 }
 public static void main(String[] args) {
 // Exceptions don't appear ...
 test("A", 1);
 test("B", 2);
 test("C", 3);
 test("D", 4);
 test("E", 5);
 // ... until you try to fetch the value:
 try {
 test("F", 2).get(); // or join()
 } catch(Exception e) {
 System.out.println(e.getMessage());
 }
 // Test for exceptions:
 System.out.println(
 test("G", 2).isCompletedExceptionally());
 // Counts as "done":
 System.out.println(test("H", 2).isDone());
 // Force an exception:
 CompletableFuture<Integer> cfi =
 new CompletableFuture<>();
 System.out.println("done? " + cfi.isDone());
 cfi.completeExceptionally(
 new RuntimeException("forced"));
 try {
 cfi.get();
 } catch(Exception e) {
 System.out.println(e.getMessage());
 }
 }
}
/* Output:
Throwing Exception for A
Breakable_B [1]
Throwing Exception for B
Breakable_C [2]
Breakable_C [1]
Throwing Exception for C
Breakable_D [3]
Breakable_D [2]
Breakable_D [1]
Throwing Exception for D
Breakable_E [4]
Breakable_E [3]
Breakable_E [2]
Breakable_E [1]
Breakable_F [1]
Throwing Exception for F
java.lang.RuntimeException: Breakable_F failed
Breakable_G [1]
Throwing Exception for G
true
Breakable_H [1]
Throwing Exception for H
true
done? false
java.lang.RuntimeException: forced
*/