SCJP: can't widen and then box, but you can box and then widen

Question

I\'m studying for the SCJP exam and I ran into an issue I can\'t really wrap my head around.

The book says you can\'t widen and then box, but you can box and then wi

Answer 1

the language is confusing.

Basically you can't go in this fashion:
byte -> Byte -> Long
because Byte and Long don't share an is-a relationship.
So, it tries to do this:
byte -> long -> Long
But it can't do that either(apparently due to compiler limitations). So, it fails and throws an error.

But, on the other hand you CAN do this:
byte -> Byte -> Object
because Byte is-an Object.

consider 2 functions and a byte variable:

toLong(Long x)
toObject(Object x)
byte b = 5;

Then this statement will be illegal:
toLong(b);
// because b -> new Byte(b) -> new Long(new Byte(b)) is illegal.
AND byte -> long -> Long can't be done due to compiler limitations.

but this statement is legal:
toObject(b);
// because b -> new Byte(b) -> new Object(new Byte(b)) is legal.