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I have some confusion about generic programming in java:
If Manager is subclass of Employee,
Collection<Manager> managers=new Collection<Manager>;
Collection<Employee> employees=managers;//why illegal?
Why the last statement is illegal?
Since according to illustration in the book CORE JAVA,after
the erasion,Collection<Manager> and Collection<Employee> are
all converted into raw type Collection.
If the above were true, then you could take your collection of managers, treat it as a collection of employees, and then put any employee into a collection of managers (i.e. not just a manager, but a (say) graduate trainee, a CIO etc.)
It’s a little counter-intuitive. An orange is a fruit. A list of oranges is not a list of fruit (otherwise you could put an apple in it). There’s a concise explanation in the Java Generics Tutorial.