# How do i make a crash handler?

**URL:** <https://discourse.processing.org/t/how-do-i-make-a-crash-handler/41387>\
**Category:** Coding Questions\
**Created:** [March 21, 2023, 3:57pm UTC](https://discourse.processing.org/t/how-do-i-make-a-crash-handler/41387 "2023-03-21T15:57:15Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Aryszin](https://avatars.discourse-cdn.com/v4/letter/a/ec9cab/32.png) [@Aryszin](https://discourse.processing.org/u/Aryszin)\
**Post date:** [March 21, 2023, 3:57pm UTC](https://discourse.processing.org/t/how-do-i-make-a-crash-handler/41387/1 "2023-03-21T15:57:15Z")

</div>

Possible to make a crash handler that displays error logs?

---

<div class="post-metadata">

**Author:** ![josephh](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/josephh/32/210_2.png) [@josephh](https://discourse.processing.org/u/josephh)\
**Post date:** [March 21, 2023, 4:36pm UTC](https://discourse.processing.org/t/how-do-i-make-a-crash-handler/41387/2 "2023-03-21T16:36:03Z")

</div>

Hi @Aryszin,

One solution is to wrap the entire `draw()` function content with a [`try` / `catch`](https://processing.org/reference/try.html) block:

```processing
void drawMayRaiseErrors() {
  if (frameCount % 2 == 0) {
    int a = 5 / 0;
  } else {
    assert 0 == 1;
  }
}

void draw() {
  try {
    drawMayRaiseErrors();
  } catch (Exception exc) {
    println("Exception: " + exc);
  } catch (Error err) {
    println("Error: " + err);
  }
}

```

```auto
Exception: java.lang.ArithmeticException: / by zero
Error: java.lang.AssertionError
...

```

Note that it catches both exceptions and errors since they do not inherit from the same base class.

Also note that it only catches errors in the `draw()` function and not exceptions thrown in a library or the Processing code itself.

---

<div class="post-metadata">

**Author:** ![quark](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/quark/32/26_2.png) [@quark](https://discourse.processing.org/u/quark)\
**Post date:** [March 21, 2023, 6:03pm UTC](https://discourse.processing.org/t/how-do-i-make-a-crash-handler/41387/3 "2023-03-21T18:03:55Z")

</div>

There are different types of error

1. **Syntax errors**

- in Java these prevent the sketch being executed and are picked up in the IDE
- in Javascript they are only detected when executing the code containing the error and generally cause the program to crash.

1. **Logic errors**

- the program executes but does not work as expected (these can be bastards to debug because there are no error messages)

1. **Runtime errors**

- these are caused by the unexpected e.g. division by zero, opening a non-existent file, array out of bounds … almost always they cause the program to crash
- in most cases these errors throw exceptions which can be caught using `try - catch` statements. If they are not caught by the program they get caught by the system which stops the program and depending on your IDE prints a stack trace indicating the type and cause of the exception.

If you want to log these exceptions then you need to catch them, but then if you _can_ catch them you can prevent the program crashing in the first place. 😁