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It looks like they are mostly in Scala. It does say in the beginning of the book:
You can create web applications using Play in more than one programming language.
Both Scala and Java are first class citizens in Play: Play also exposes ideomatic Java
APIs, for programmers who want power right out of the box, while the Scala API
provides advanced language features such as pattern matching and implicits.
Although Play 1.0 was originally written in Java, Play 2.0 has been completely rewritten
from the ground up in Scala, for better perform
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