Which came first, Java or Windows?

Windows came first, by 10 years. Microsoft shipped Windows 1.0.

Side by side

Java

Java was announced in May 1995, having started in 1991 as a project called Oak aimed at interactive television — a market that did not exist yet. Its promise was "write once, run anywhere", achieved by compiling to bytecode for a virtual machine rather than to a specific processor. JavaScript arrived seven months later and was named after it purely as a marketing decision; the two languages are unrelated.

Windows

Windows 1.0 shipped in November 1985, twenty-two months after the Macintosh, and it was not an operating system — it was a graphical shell running on top of MS-DOS, and remained so until Windows NT in 1993 and the consumer transition with Windows XP in 2001. Version 1.0 could not even overlap windows: they tiled, because Apple's legal position on overlapping windows was unresolved.