java - Declaration difference between ArrayList and collection -


this question has answer here:

what's difference between following both ways

  1. collection<string> obj = new arraylist<string>();
  2. arraylist <string> obj = new arraylist<string>();

simple: in first case "forget" created arraylist - "remember" obj has properties of implements collection interface.

and should rather going for: 

list<whatever> items = new arraylist<>();
  • yes, typically want "forget" kind of specific list class created - want remember list
  • you want never use raw types (meaning: never omit generic type parameter) when dealing collections of any kind

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