Friday, 1 December 2017

java - Why List is not acceptable as List?





Consider below method
doSomething(List) which accepts
List as
parameter.



private void
            doSomething(List list) {
 // do
            something
}


Now
            consider below code snippet which tries to call doSomething()
            where I try to pass List to
            doSomething()


List
            objectList;
List
            stringList;

doSomething(stringList); // compilation error
            incompatible types
doSomething(objectList); // works fine
            


Even below code
            throws compilation error
            


objectList = stringList; //
            compilation error incompatible
            types


My question is
            why List can not be passed to a method which
            accepts List?


            
 
Answer

            

This generic question in Java may look
            confusing to any one who is not very familiar with Generics as in first glance it looks
            like String is object so List can be used where
            List is required but this is not true. It will
            result in compilation error. 


It does make sense
            if you go one step further because List
            can store anything including
            String, Integer etc but
            List can only store
            Strings.


Also have a
            look at:             href="https://stackoverflow.com/questions/21692193/why-not-inherit-from-listt">Why
            not inherit from List?


            










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