php - Why not output I hope result in PHP7 using try and catch?

In PHP7 env, I have the follow code:

try {
    echo strlen([123]);
} catch (Exception $e) {
    echo 'error...';
}

Because [123] is not string, I want it to output error..., but it outputs:

Warning: strlen() expects parameter 1 to be string, array given

Why?