CoroutineExceptionHandler in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is CoroutineExceptionHandler in Kotlin coroutines?

CoroutineExceptionHandler is a special interface in Kotlin that lets you handle uncaught exceptions in coroutines. It acts like a global error catcher for coroutine failures.

beginner

How do you add a CoroutineExceptionHandler to a coroutine?

You create a CoroutineExceptionHandler instance and add it to the coroutine context using the + operator when launching the coroutine.

Example:<br>val handler = CoroutineExceptionHandler { _, exception -> println("Caught: $exception") }<br>GlobalScope.launch(handler) { /* code */ }

intermediate

When does CoroutineExceptionHandler catch exceptions?

It catches exceptions only from uncaught exceptions in root coroutines or coroutines launched with launch. It does not catch exceptions from async coroutines because those exceptions are deferred until you call await().

beginner

What happens if you don't provide a CoroutineExceptionHandler?

If no CoroutineExceptionHandler is provided, uncaught exceptions in coroutines are handled by the default exception handler, which usually prints the stack trace and may crash the application.

intermediate

Can CoroutineExceptionHandler handle exceptions from async coroutines automatically?

No. Exceptions from async coroutines are captured and only thrown when you call await(). You need to handle them with try-catch around await() or use other mechanisms.

What is the primary role of CoroutineExceptionHandler in Kotlin coroutines?

A To catch uncaught exceptions in coroutines

B To start a new coroutine

C To cancel running coroutines

D To delay coroutine execution

CoroutineExceptionHandler is designed to catch uncaught exceptions in coroutines.

Which coroutine builder's exceptions can CoroutineExceptionHandler catch automatically?

A <code>runBlocking</code>

B <code>async</code>

C <code>launch</code>

D <code>withContext</code>

Exceptions from launch coroutines are caught by CoroutineExceptionHandler. Exceptions from async are deferred.

How do you add a CoroutineExceptionHandler to a coroutine?

A By adding it to the coroutine context with the <code>+</code> operator

B By calling a special function inside the coroutine

C By wrapping the coroutine in a try-catch block

D By using <code>runCatching</code> on the coroutine

You add CoroutineExceptionHandler to the coroutine context using the + operator when launching the coroutine.

What happens if an exception is thrown in an async coroutine and you don't call await()?

A The exception is ignored

B The exception is caught by <code>CoroutineExceptionHandler</code>

C The exception crashes the program immediately

D The exception is not thrown until <code>await()</code> is called

Exceptions in async coroutines are deferred and only thrown when await() is called.

If you want to handle exceptions from an async coroutine, what should you do?

A Add a <code>CoroutineExceptionHandler</code>

B Use try-catch around <code>await()</code>

C Use <code>launch</code> instead of <code>async</code>

D Ignore exceptions because they are handled automatically

Exceptions from async must be handled by try-catch around await().

Explain what CoroutineExceptionHandler is and how it works in Kotlin coroutines.

Think about how exceptions behave differently in launch and async coroutines.

Describe a scenario where CoroutineExceptionHandler would not catch an exception and how you would handle it.

Focus on async coroutines and deferred exceptions.