i didn't know that java applets can use opengl. i guess that's why you have to accept this security certificate.

i think it's possible.

the rendering really is quite simple like schokokeks said. there is no advanced occlusion culling or visibility calculation going on. there is no need for it. you just can't use an entity per block but have to use bigger chunks and create your own meshes (for example 16x16x16 blocks are one entity like in my experiment). that's how minecraft does it. in the debug display you even always can see "mesh of 4 chunks updated" or something like that.

edit:
the disadvantage of superku's method is that you never know how many entities you will need. the entity handling would get quite complicated if you want to achieve big worlds and in worst case too many entities could be required.