Editing Apache Groovy (section)

===Traits===
According to Groovy's documentation, "[[Trait (computer programming)|Traits]] are a structural construct of the language that allows: composition of behaviors, runtime implementation of interfaces, behavior overriding, and compatibility with static type checking/compilation."

Traits can be seen as [[interface (object-oriented programming)|interface]]s carrying both default implementations and state. A trait is defined using the trait keyword:

<syntaxhighlight lang="groovy">
trait FlyingAbility { /* declaration of a trait */
  String fly() { "I'm flying!" } /* declaration of a method inside a trait */
}
</syntaxhighlight>

Then, it can be used like a normal interface using the keyword <code>implements</code>:

<syntaxhighlight lang="groovy">
class Bird implements FlyingAbility {} /* Adds the trait FlyingAbility to the Bird class capabilities */
def bird = new Bird() /* instantiate a new Bird */
assert bird.fly() == "I'm flying!" /* the Bird class automatically gets the behavior of the FlyingAbility trait */
</syntaxhighlight>

Traits allow a wide range of abilities, from simple composition to testing.