Other have already given their comment and I agree with them. but to add, as much as Java replaced C and C++, others will replace Java.

There is no doubt that .NET is very successful in presentation tier and web components, and Java ee still has not pull itself together for presentation tier well, but the level of integration that exist in competitor frameworks (Java ee) is quite high as well. in today's industries the main intention of such frameworks (.net and Java ee) is to provide the best way to integrate and interoperate with other systems (either legacy or newly developed). neither are talking about replacing. Even when Microsoft goes to conferences (they are called architect / developer evangelists) to talk people into their new features their intention is never to convince people to replace their products because they already know it does not make sense.

Java has been evolved so much that it seems to be hard and unreasonable to leverage other platforms functionality to reach to this level. so far it seems to be waste of time and money to do so. Also as Arash has pointed out, some platforms e.g. Windows and Unix family have already shown which frameworks are more suitable.

After all these are all architecture decisions but from this perspective, it seems difficult to replace such competitors.