Difference Betwixt A Listing Together With Arraylist Reference Variable Inwards Java?

Someone who is only starting amongst Java programming linguistic communication oft has dubiety close how nosotros are storing an ArrayList object inwards List variable, what is the divergence betwixt List in addition to ArrayList? or why non only shop the ArrayList object inwards ArrayList variable only similar nosotros create for String, int, in addition to other information types. Well, the principal divergence betwixt List in addition to ArrayList is that List is an interface spell ArrayList is a class. Most importantly, it implements the List interface, which likewise agency that ArrayList is a subtype of List interface. In Java or whatsoever object oriented language, super type of variable tin shop an object of subtype. This is known equally Polymorphism because whatsoever virtual method volition move executed from subclass only, fifty-fifty though they were called from super type. This is the beginning, similar a shot let's meet those 2 questions equally well.

Why shop ArrayList object on List variable?

You powerfulness receive got seen something similar this:

List<Movie> listOfMovies = new ArrayList<Movie>()

hither nosotros are using a List equally a type of variable to shop an object of ArrayList class, created using new() operator. This is known equally programming for the interfaces. In fact, everywhere yous quest to declare a reference variable, yous should ever purpose the supertype e.g. Map for passing HashMap, Set for passing HashSet in addition to List for passing ArrayList, LinkedList or Vector. You should purpose interface equally type on the supply type of method, type of arguments etc equally shown below? Now big interrogation comes, Why should yous create that?



The answer is to accept payoff of Polymorphism. If yous purpose interface than inwards time to come if the novel implementation is shipped in addition to hence yous are non required to alter your program. For example, whatsoever plan written using List volition operate equally expected whether yous exceed a LinkedList, Vector or ArrayList, because they all implements List interface, they obey the contract exposed past times List interface.

The alone divergence comes inwards performance, which is truly on of the driver for change. In short, if yous plan using interface, tomorrow if a ameliorate implementation of your interface is available in addition to hence yous tin switch to that without making nay farther alter on the customer side (part of the plan which uses that interface).


Similarly, yous should purpose interface type on method arguments:

public void sort(List<? extends Comparable> input){        // logic to form the listing   }

in addition to purpose interface type on the supply type of methods:

public List<Employee> getEmployees(int departmentId){        // logic to supply employees for a given department }

If yous shop ArrayList's object into a reference type of ArrayList, equally shown below in addition to hence your code volition non operate if yous exceed a LinkedList, because ArrayList IS NOT a LinkedList.

public List<Movies> getMovies(LinkedList<String> actors){        // this code volition non operate if yous exceed ArrayList }
 

but next code volition work, fifty-fifty if yous exceed ArrayList, Vector, CopyOnWriteArrayList or LinkedList, because it expects a List, which is an interface:

public List<Movies> getMovies(List<String> actors){        // this code volition operate if yous exceed ArrayList, Vector etc }

Your plan is pretty much difficult coded, it lack the flexibility offered past times Polymorphism in addition to Inheritance. This answer is likewise applicable to questions similar divergence betwixt Map in addition to HashMap or Set in addition to HashSet because ultimately they are the same question, the divergence betwixt interface in addition to their implementation. You must follow SOLID principles to write a ameliorate plan inwards object oriented programming languages similar Java or C++.

Here are 10 object oriented principles Every Java Developer should know

Further Learning
Java In-Depth: Become a Complete Java Engineer
Java Fundamentals: Collections
Data Structures in addition to Algorithms: Deep Dive Using Java
Algorithms in addition to Data Structures - Part 1 in addition to 2
Data Structures inwards Java nine past times Heinz Kabutz

Share this post