52. Catching Errors

Before we go too far on this one please note that errors indicate serious/abnormal problems and shouldn’t be caught.

Errors are different to exceptions as they indicate a fundamental issue rather than a recoverable problem. It’s highly unlikely you’ll ever need to handle an error so treat it like a cold and don’t try to catch one. They may “crash” your program but it’s likely any treatment that you try to apply will make things worse. For example, if somehow you managed to catch a java.lang.OutOfMemoryError, how would you respond?

One more time: don’t catch errors.

Errors are objects and can be caught much like exceptions but the following won’t work:

try {
    assert true == false
} catch (err) {
    println 'I caught the error!'
    println err.message
}

The code above doesn’t do what we hoped as, by default, the catch is looking for Exception or one of its subclasses¹ - probably because we shouldn’t catch errors.

In order to catch an error we must provide Error (or a subclass of Error) as the data type in the catch:

try {
    assert true == false
} catch (Error err) {
    println 'I caught the error!'
    println err.message
}