collections - Polymorphism in Java -

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why uses polymorphism in java while using collections.

what difference between these initializations.

  private list<order> orderlist = new arraylist<order>();   private arraylist<order> orderlist = new arraylist<order>();

in second form, orderlist can treated arraylist<order> or inheriting arraylist<order>.

in first form, orderlist treated list<order> , recommended when use functionality defined list<t> interface. way code more flexible , can refactored (e.g. realize need linkedlist<t> instead, change initialization , of code not need changed).

also, helpful code refactoring use interfaces instead of actual types, if possible (e.g. use parameters of type list<t> instead of arraylist<t>), because allows caller change list type without changing in called function.


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