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I likeThatMeow
Asked: 2020-08-28 21:38:17 +0800 CST 2020-08-28 21:38:17 +0800 CST

List interface with different instantiations

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What is the difference, advantages, disadvantages between:

  1. List a=new ArrayList();\\suponiendo que introducire numeros enteros
  2. ArrayList a=new ArrayList(); \\suponiendo que introducire numeros enteros
  3. ArrayList<Integer> a=new ArrayList<Integer>();
  4. List <Integer> a=new ArrayList<Integer>();

Or are they all equivalent?

Note: instead of ArrayListcould also have been LinkedListor someone else.

java

2 Answers

  1. Best Answer

    The difference lies in what each thing is:

    • Listis an interface (which extends interface Collection)
    • ArrayListis a class (which implements the interface List)

    Although all the options you specify will work correctly, using the interface Listhas advantages over using the implemented class ArrayListbecause you might benefit from polymorphism in object-oriented programming.

    For example, if later in your project you see that you need to change the implementation, if you've defined your variable as Listyou shouldn't have much of a problem changing from ArrayListto another type of class that implements the interface List( LinkedListfor example). That is why options 1 and 4 may be more advantageous.

    And now, to define the type parameter of the list (options 3 and 4) or not to define it (options 1 and 2)... it's going to depend on what you want to do. If you define it, then the types will be validated at compile time, which can help you find errors, but will give you less flexibility later.

    As it seems that you are clear about what you are going to use Integerand not others, then perhaps it is better for you to define the type (option 4), because it will make the code easier to maintain and debug.

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  2. In principle they are all equivalent, that is, the difference between one and the other does not affect you when compiling. But internally there is a difference and it is that at run time, the list will be instantiated as Object.

    Anyway, I recommend you to instantiate it as ArrayList, so everything is clearer.

    Greetings.

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