Java does not monomorphize, it has no true generics - it's objects all the way down. It does, however, perform guarded devirtualization since all methods are virtual by default, so performance lives and dies by OpenJDK hotspot emitting guarded for fast, often multiple, dispatch as well as optimizing "megamorphic" callsites with vtable-ish dispatch (which is about the default cost of interface dispatch in .NET, somewhat slower than virtual dispatch).