As of December 2015 it remains possible to download and install the latest version of Java on Windows XP. However, Oracle stopped officially supporting XP in April 2014. Java.com states that users may still use the latest Java on Windows XP but without support and at their own risk.
Oracle dropped Windows XP in April 2014, the same time as Microsoft ended support for the aging OS. Oracle recommends that users update to a supported of Windows. However, the Java auto-update functionality is still live for XP users, and security patches are still pushed out.
Java is available for download for Windows XP via Java.com. As of December 2015, the latest version of the runtime is Version 8 Update 66.