Next we’ll continue exploring Java exceptions.
First, we’ll look at how we can
throw our own exceptions.
Next, we’ll discuss the different types of Java exceptions and how they are used.
Aren’t errors fun?
Let’s do this.
Last time we looked at
try-catch, Java’s syntax for handling exceptions.
But where do exceptions come from?
Some exceptions are generated directly by Java.
For example, executing this code will generate a
However, Java also provides a way for us to
throw exceptions directly—the
Let’s see how that works.
Java has several built-in exceptions that you may find useful in your own code.
throw is particularly useful when there is no valid way to continue.
Maybe your method has received bad input, or encounters a situation that it is unprepared to handle.
We’ll discuss this more in future lessons.
As a initial example, many of the situations that we’ve been handling using
assert are better handled using the
Let’s look at an example:
In Java the
Throwable class is the superclass of all objects that can be thrown, either using
throw or in case of an error like a null pointer exception.
Throwable has three important subclasses that are handled differently in Java: checked exceptions, unchecked exceptions, and errors.
Let’s look at each category in turn. First, let’s browse the documentation together!
Checked exceptions in Java must be handled.
The compiler will check and enforce this!
They are always generated using
throw, which is how the compiler knows where they are and when you need to handle them.
Exception class itself is checked, as are most of its descendants.
Let’s see a example of checked examples.
(Note that this example uses a playground that works a bit differently than the ones that we’ve used previously. I’ll explain why in the walkthrough.)
Unchecked exceptions don’t need to be handled. But, the reason for this is that, in many cases, they arise from programmer error. Let’s look at some examples.
The final category are Java errors. These are serious problems that you should not try to handle. According to the documentation:
An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch. Most such errors are abnormal conditions.
However, it is worth noting that
assert generates an error.
It is also possible to generate errors through programming errors, like this one:
This generates a
You may get much more familiar with this kind of error soon…
Timnit Gebru’s is the co-founder of Black in AI and the founder of the Distributed Artificial Intelligence Research Institute. Her work identifying bias in artificial intelligence and leadership drawing attention to ethical issues in AI prompted her abrupt departure from Google, specifically due to work that she and co-authors hoped to publish drawing attention to weaknesses and biases inherent in large langauge models. That work seems even more relevant today, with the rise of GPT-3, ChatGPT, and the growing use of large language models in other contexts and for a wide variety of purposes.
In the video below, she discusses one component of her work, specifically improving the understanding of the datasets used to train and generate AI models:
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