My bad, I think they are called Generics in Java. I always thought of these as the same thing, just with different names in different languages, is that wrong?
Templates and generics are very different. Afaik Templates generate specialised code for each invocation of that template with a different type.
Java uses Type Erasure for Generics, which means that generic type variables are checked at compile time, but that type information is not available at runtime. At compile time you may have List<Foo> and List <Bar> but at runtime its all just List<Object> (Object being the base type everything inherits from). Basically List stores a bunch of pointers to objects and since pointers can point to anything a List can basically "store" anything.
Then you have a divide between primitives and Objects in Java, where primitives are double, int, boolean etc.. Primitives are types in the C-sense, e.g. int is nothing more than a 32-bit number, not a class in the Java-sense. But since ints are not classes and as such do not inherit from Object, they cannot be placed inside of List<Object>. Therefore there cannot be a List<int>. But there is Integer, which is an Object-wrapper around an int, meaning you can have a List<Integer>. This is called boxing and like all indirection carries a performance penalty.
Java hopes to heal this rift between primitives and Objects through something called Project Valhalla which has been 10 years in the making and is expected to land in the next two years or so.
