When and where to use different Java Collections FrameWorks Part I

This post focus on when are where to use different Java collections interafce and class.
1. ArrayList<E> is a mostly used if we want fast, random access of the elements.

Example . Suppose you have a data of different students grouped by department, you have a task to add new internation students all with their first name started with O and last name ending with A, whereas in the system, student are arranged in alphabetical order with their first name.

public class Student
    private List<String> students = new ArrayList<>();

    public List<String> addNewStudent( String fullName )
        return students;
    public Integer studentInsertionID ( String studentName )
        char firstLetter = studentName.charAt(0);
        return Integer.valueOf(firstLetter);


ArrayList offers constant time for the following operations: size, isEmpty, get, set, iterator, and listIterator; amortized constant time for the add operation; and linear time for other operations.
2. LinkeList<E>

we can consider using a LinkedList if fast adding and removing elements at the end of the list is required.
Example : In a shopping software system, you are requested to have a %20 discount on each products price by the arrival of the shopper he gets %20 ( * n ) discount [ where n = totalNumber of user], example if the first user access the system for a product os price $500 , he gets $500 ( 20 * 1 ) % = $100 , the second user wants to purchase $400 , he gets $400 ( 20 * 2 ) % = $160 , for third shopper buying a product worth $1500 = $1500 ( 20 * 3 ) = 900 … till the end

Do you notice addition and manipulation of new data from the end ?

Exactly ! LinkedList<E> is a perfect soltution to such probelm

public class Store
    public String discount ( double productPrice )
        double newPrice = 0.01 * productPrice * Math.multiplyExact(20,shoppersArrival());
        if ( newPrice >= productPrice )
            return String.format("Processing #%.2f....\nSorry!!! No discount for you, because you are the number %d shopper , your product price is %.2f . ",productPrice,shoppersArrival(),productPrice);
            return String.format("Processing $%.2f....\nWao!!! Your product discount price is %.2f, because you are the number %d shopper .",productPrice,newPrice,shoppersArrival());

    public Integer shoppersArrival()
        int n = 10;
        return n ;

    public List<String> byDiscount ( String shoppersFullName )
        List<String> addShoppersFromBack = new LinkedList<>();
        return addShoppersFromBack;

The both variables use add method but their run time for manipulation of data varies . Hope you enjoy this ? Why not reading the part II of this post …


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