A bit of background on DNS: (apologies for the oversimplification)

DNS is the internet "Domain Name Service". It provides the mapping between computer names and computer addresses. For example, the name ds.internic.net has the 3 IP addresses, 198.49.45.10, 192.20.239.132, and 204.179.186.65. Probably, each IP address eventually is mapped onto a different computer, although multiple IP addresses could also map onto a single computer. The reason for many-to-many name-to-address mappings is that it enables system administrators to balance the network load on their machines. The name ds.internic.net is probably accessed hundreds of thousands of times every day by people all over the network, so it makes sense for that one name to be served by multiple machines with multiple IP addresses.

Let's use the term "DNS spoofing" to mean that a computer on the internet has been able to advertise a false IP address for itself. DNS spoofing isn't directly related to Java, but might be used as part of a Java attack applet.