Weakest type

• For inputs

  • Instead of conreate impl, use interfaces

  • instead of ArrayList, use List, or Collection (if dont care about ordering) or ITerable (if dont care about the size)

    • This gives the user more flexibility, can use method with ArrayList, LinkedList etc

    • Reduces need to add more convience methods for different methods

    • avoids overloading

• For return type

  • Does it matter the need for the concreteness of impl or sub class with extra properties/behaviour

• Make the type more abstract, allows for change in implementatoin of api, without breaking the user

  • more flexibility

• As the signature is a contract with the user.

  • if the contract says the return type is a collection, and the user is uses this as so, then they are breaking the contract, not the developer