Why is my loop not retrieving the last items?

Question

I am trying to implement a method to view a list of items and their quantities, without being repeated. I am doing this using ArrayList which will hold objects of the type Item which I created. The Problem is in the loop where I remove duplicates from the a copy of the original list as it doesn't show the last two Items in the list and I don't know how to fix it. Here is the code. Item is very simple object, it contains (int identifier, int price, String name)

private ArrayList list;

public void print(ListOfItems storeList)
{
    list = storeList.getList();
    if ( list.size() == 0)
        System.out.println("Sorry! There are no available Items at the store at this moment.");
    /** I changed this section
    else
    {
        Object[] originalItems = list.toArray();
        ArrayList copy = storeList.getCopy(storeList.getList());
        Object[] copyItems = copy.toArray();
        System.out.println("Here is a list Of available items in this Store");
        System.out.println("Name\tIdentifier\tprice\tQuantity");

       //this loop is wrong
        for (int i = 0; i < originalItems.length-1; i++)
        {
            for (int j = i+1; j < originalItems.length; j++)
            {
                if (originalItems[i].equals(originalItems[j]) && copyItems[j] != null)
                {
                    copy.remove(originalItems[j]);
                }
            }
        }
        **/
        //Below is the write loop
        else
        {
        Object[] originalItems = list.toArray();
        ArrayList copy = new ArrayList(list.size());
        for (int i = 0; i < originalItems.length; i++)
        {
            Item item = (Item) originalItems[i];
            if (copy.contains(item) == false)
            {
                copy.add(item);
            }
        }

        Object[]cop = copy.toArray();
        for (int i = 0; i < cop.length; i++)
        {
            if (cop[i] != null)
            {
                Item item = (Item) copyItems[i];
                System.out.print(item.getName() + "\t");
                System.out.print(item.getIdentifier() + "\t\t");
                System.out.print(item.getPrice() + "\t");
                System.out.print(Methods.getOccurences(list, item));
                System.out.println();
            }
        }

        System.out.print("*****************************");
    }
}

Here is the class for ListOfItems

import java.util.ArrayList;
public class ListOfItems 
{
int numOfItemsInStore = 50;
private ArrayList list = new ArrayList(numOfItemsInStore);
public ListOfItems()
{
    Item item1 = new Item (111, 50, "Item1");
    list.add(item1);
    Item item2 = new Item (222, 99, "Item2");
    list.add(item2);
    Item item3 = new Item (333, 20, "Item3");
    list.add(item3);
    Item item4 = new Item (444, 199, "Item4");
    list.add(item4);
    Item item5 = new Item (555, 14, "Item5");
    list.add(item5);
    Item item6 = new Item (666, 40, "Item6");
    list.add(item6);
    list.add(item6);
    list.add(item6);
    list.add(item2);
    list.add(item3);
    list.add(item3);
    list.add(item3);
}

public ArrayList getList()
{
    return list;
}


public ArrayList getCopy(ArrayList listToCopy)
{
    ArrayList copy = new ArrayList(numOfItemsInStore);
    if (listToCopy.isEmpty())
        System.out.println("This list is Empty");
    else
    {

        Object[] listArray = listToCopy.toArray();
        for (int i = 0; i < listArray.length; i++)
        {
            Item item = (Item) listArray[i];
            copy.add(item);
        }
    }

    return copy;
}
}

here is the Item class

public class Item 
{
private int identifier;
private int price;
private String name;

public Item (int id, int price , String name)
{
    this.identifier = id;
    this.name = name;
    this.price = price;
}

public int getIdentifier()
{
    return identifier;
}

public int getPrice()
{
    return price;
}

public String getName()
{
    return name;
}
}

Answer 1

Okay first of all I would suggest to use a Set to remove duplicates...

public void print(ListOfItems storeList)
{
    // At this point make sure that "getCopy(ArrayList <Item> listToCopy)" creates a deep copy!
    ArrayList <Item> copyOfList = storeList.getCopy(storeList.getList());

    // For using this statement make sure that you override "equals" in the "Item" class!
    Set <Item> uniqueItems = new HashSet <Item> (copyOfList);

    for(Item item : uniqueItems)
    {
        // Code for usage of each single item
    }
}

...This is just one possible approach of solution, but makes sure that you overrides equals and that your function getCopy() creates a deep copy!

Thanks to Coderino Javarino , of course you must override the equals and the hashCode method not the toString method!

One option to override the equals method...

@Override public boolean equals(Object object)
{
    if(this == object)
    {
        return true;
    }

    if(object == null || getClass() != object.getClass())
    {
        return false;
    }

    Item item = (Item) object;

    return Objects.equals(this.name, item.name) &&
         this.identifier == item.identifier &&
         this.price == item.price;
}

And here an option to create a deep copy...

public ArrayList getCopy(ArrayList <Item> listToCopy)
{
    if(null == listToCopy)
    {
        // Handle this option too
    }

    ArrayList <Item> copy = new ArrayList(listToCopy.size());

    for(Item item : listToCopy)
    {
        // It is important that your class "Item" contains a copy constructor
        copy.add(new Item(item));
    }

    return copy;
}

Answer 2

According to your code, I guess item 6 and item 3 were missed from your final cop list. Because remove action is not correct.

At the begin for-loop, the initial state of 3 variables are:

• originalItems: [1,2,3,4,5,6,6,6,2,3,3,3]
• copy: [1,2,3,4,5,6,6,6,2,3,3,3]
• copyItems: [1,2,3,4,5,6,6,6,2,3,3,3]

The state of 3 variables above after outter for-loop finished round 6 (i=5):

• originalItems: [1,2,3,4,5,6,6,6,2,3,3,3]
• copy: [1,2,3,4,5,6,2,3,3,3] <- two item 6 were removed, it worked as expect
• copyItems: [1,2,3,4,5,6,6,6,2,3,3,3]

Unluckily, when i=6 and j=7, we found that "item 6" is duplicate again, and the copy list removed it. <- the problem is here.

We are absolutely able to explain why "item 3" lost with the same idea. It happened when i=10, j=11.

And how to fix it? If you still want to use 2 for-loop, you can implement the strategy below:

init copy list is empty
init originalitem as copy of your list
for item in originalItem
   isExist = false
   for copy list
       if item in copy
           isExist = true
           break
   if isExist = false
       copy add item 

But, there are many ways to remove effectively a duplicate element in a list, rather than using 2 for-loop strategy.

Answer 3

    else
    {
        Object[] originalItems = list.toArray();
        ArrayList copy = new ArrayList(list.size());
        for (int i = 0; i < originalItems.length; i++)
        {
            Item item = (Item) originalItems[i];
            if (copy.contains(item) == false)
            {
                copy.add(item);
            }
        }