Java type casting generics list of list of child to list of list of parent -

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• how cast list of supertypes list of subtypes? 14 answers

i have class childdata1 extends data. how can convert list<list<childdata1>> list<list<data>> ?

under rules of generics can following assignment without cast:

list<list<childdata>> subclasslist = ... list<? extends list<? extends data>> superclasslist = subclasslist;