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Maybe it's now an option to avoid NullPointerException?

NullPointerException is an obvious runtime problem in most Java applications. But it's not limited to Java, in PHP for example we could get a "Trying to get property of non-object". But today, there's a compilation alternative to this runtime problem.

Maybe Cat | Option[Cat] | Optional<Cat>

Scala is a modern functional (and Object Oriented) language based on the JVM. I did a lot of Scala during the past year, mostly with the Spark framework for distributed computing. In Java, if you try to access a element in a Map<String, Cat> for example, the signature will look like this:

 * Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
 * @return Cat or null
public Cat get(String key);

And it's correct (for the compiler) to write:


If the Cat is here, it's fine. If he's not, the program crash with a NullPointerException. The compiler will not help you to catch this kind of bugs.

In Scala the signature for a type Map[String, Cat] is:

def get(key: String): Option[Cat]

So you cannot write something like before. The compiler will not allow it because the object Option[Cat] doesn't have a miaou method. So, how did we manage this? We use pattern matching to check the None option. Indeed, the Option[Map] type is divided into two types: Some[Cat] and None.

this.get("Schroedinger") match {
  Some(cat) => cat.miaou()
  None      => // do something

Scala is not a strict language so it's possible to get the content of an option or a null with the get method on Option[Cat]:

// throw a NullPointerException

This concept of optional type come from functional programming. The last version of Java introduces a lot of functional programming stuff, it's now possible to use the new type: Optional<Cat>.

And, last but not least, it's not a new hype feature from 2015, some great (and old) languages like Haskell has the Maybe type for a long time. Maybe Cat could be Just Cat or Nothing.

In conclusion, if you want to know more about this amazing functionality: