Class (a.class b.class etc)

Class are function to core of game

obfuscated via obfuscator

Notch obfuscated to hide the names of methods, variables such as com.mojang.minecraft.b.b and classes.

as indev, Notch and Dock renamed Level.class and Entity.class and Mob.class excluding MinecraftApplet to protect form hackers cracking game or editing or creating mods in indev.

stack trace prints in obfucasted names like com.mojang.minecraft.e.run(Unknown Source)

java decomplier can view classes

for deobfuscated see Debobfcasted_Clients