The meaning of Java code (Object[])(Object[])arrayOfBytes[1]

There is no point of doing so. Makes no extra difference but just kills the readability and causes confusion.

There's no good reason to apply the same cast twice, it's simply an error*/quirk of the original author.

There are very few places where a double-cast even with different types is meaningful. But with the same type, no, no point to that at all.

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* (a fairly harmless one, though it's not pretty)

I assume this is just a "bad" (in meaning of style and unnecessary) programming.