Technically speaking, Java can have mixins as well if you include libraries that provide it. Stuff like Spring AOP uses aspectj under the covers and you can mimic mixin-like functionality in your classes with a few annotations here and there.
Technically, you could also provide mixins through the decorator pattern and interfaces. IntelliJ (and I am sure Eclipse) can generate this for me. However, that's less elegant and more fragile than using a language (e.g. Scala) which has Mixins as a language feature: IntelliJ can write code for me, but it can't read for me, nor can it explain it to other developers.
Likewise, I can use multiple inheritance in C++ exclusively only to mimic interfaces (as purely virtual classes) or Mixins (and in fact a lot of corporate style guidelines, e.g. Google's explicitly say that), but it isn't quite the same as having these as language features.
