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// concurrent/CompletableExceptions.java

// (c)2021 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

*/