[newmana]

They might be talking about the checkcast operation: https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-6.ht...

This is generated when you do something like: final Main value = list.get(0);

http://henrikeichenhardt.blogspot.com/2013/05/how-are-java-g...

[xxs]

The cast is added by javac, so it just needs to verify the object on the stack to be compatible w/ the provided class. That part is very simple.