Under GPLv2, under which OpenJDK is distributed, that is technically optional. You basically have two options:
a) Ship the source code alongside the binary
b) Offer to furnish the source code to people who ask for it
AFAIK, the second option was intentionally introduced to provide for a delay in releasing source code, since providing the source code to uninterested parties might be cost-prohibitive if it's 1992 and you're publishing on floppies.
If so, then we need to wait until somebody got a copy of it and then distribute it. Since GPLv2 should have clauses prohibiting the any parties from baring redistribution given the same license is used.
But just one thing... according to Wikipedia [1] it is actually based upon Hotspot, but they also entered an undisclosed agreement. In such aspect, Azul may have licensed Hotspot not through GPLv2 but through different terms with Oracle. If that is true, they may be able to keep part of their code out of GPLv2.
Also they had some open source stuff released under GPLv2 at another website [2].
It was intentional, but not to allow for "delay". It just recognizes that many forms of "software distribution" are to parties who don't want the source code. The point is you have to give it when asked; there's no grace period in the license.
a) Ship the source code alongside the binary
b) Offer to furnish the source code to people who ask for it
AFAIK, the second option was intentionally introduced to provide for a delay in releasing source code, since providing the source code to uninterested parties might be cost-prohibitive if it's 1992 and you're publishing on floppies.