Arrays are reified in Java

Question

I recently came across that, Arrays are reified in Java. That is, they know the type information only during run time. But I am a little confused with this definition.

Answer 1

As mentioned in doc:

A reifiable type is a type whose type information is fully available at runtime. This includes primitives, non-generic types, raw types, and invocations of unbound wildcards.

Non-reifiable types are types where information has been removed at compile-time by type erasure — invocations of generic types that are not defined as unbounded wildcards. A non-reifiable type does not have all of its information available at runtime. Examples of non-reifiable types are List and List; the JVM cannot tell the difference between these types at runtime. As shown in Restrictions on Generics, there are certain situations where non-reifiable types cannot be used: in an instanceof expression, for example, or as an element in an array.

So Arrays are reified and covariant but generics are invariant and type-erased by nature. Arrays provide runtime type safety and throw ArrayStore exception if element of correct type is not added.