HashMapIssue.java

//Custom class used as key for HashMap
public class CustomHashMapIntegerKey {

    private Integer key = 0;

    public void setKey(Integer key) {
        this.key = key;
    }

    public Integer getKey() {
        return this.key;
    }

    @Override
    public int hashCode() {
        return this.key.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (null == obj) return false;
        if (this.getClass() != obj.getClass()) return false;
        final CustomHashMapIntegerKey customHashMapIntegerKey = (CustomHashMapIntegerKey) obj;
        if (null == this.key && null != customHashMapIntegerKey.getKey()) return false;
        if (null != this.key) {
            if (!this.key.equals(customHashMapIntegerKey.getKey())) return false;
        }
        return true;
    }
}

//DepartmentItemDataObject
public class DepartmentItemDataObject {
    private Integer itemPrice, itemDiscount, itemId, orderedQuantity = 0;
    private String itemImageUrl, itemImageThumbnailUrl, itemWeightOrQuantity, nutritionFacts, itemDescription, itemName = null;
    private CustomHashMapIntegerKey customHashMapIntegerKey = null;

    public DepartmentItemDataObject() {
        this.customHashMapIntegerKey = new CustomHashMapIntegerKey();
    }

    public int getItemPrice() {
        return itemPrice;
    }

    public void setItemPrice(int itemPrice) {
        this.itemPrice = itemPrice;
    }

    public int getItemDiscount() {
        return itemDiscount;
    }

    public void setItemDiscount(int itemDiscount) {
        this.itemDiscount = itemDiscount;
    }

    public String getItemImageUrl() {
        return itemImageUrl;
    }

    public void setItemImageUrl(String itemImageUrl) {
        this.itemImageUrl = itemImageUrl;
    }

    public String getItemImageThumbnailUrl() {
        return itemImageThumbnailUrl;
    }

    public void setItemImageThumbnailUrl(String itemImageThumbnailUrl) {
        this.itemImageThumbnailUrl = itemImageThumbnailUrl;
    }

    public String getItemWeightOrQuantity() {
        return itemWeightOrQuantity;
    }

    public void setItemWeightOrQuantity(String itemWeightOrQuantity) {
        this.itemWeightOrQuantity = itemWeightOrQuantity;
    }

    public String getNutritionFacts() {
        return nutritionFacts;
    }

    public void setNutritionFacts(String nutritionFacts) {
        this.nutritionFacts = nutritionFacts;
    }

    public String getItemDescription() {
        return itemDescription;
    }

    public void setItemDescription(String itemDescription) {
        this.itemDescription = itemDescription;
    }

    public String getItemName() {
        return itemName;
    }

    public void setItemName(String itemName) {
        this.itemName = itemName;
    }

    public int getItemId() {
        return itemId;
    }

    public void setItemId(int itemId) {
        this.itemId = itemId;
        this.customHashMapIntegerKey.setKey(this.itemId);
    }

    public int getOrderedQuantity() {
        return orderedQuantity;
    }

    public void setOrderedQuantity(int orderedQuantity) {
        this.orderedQuantity = orderedQuantity;
    }

    public CustomHashMapIntegerKey getCustomHashMapIntegerKey() {
        return this.customHashMapIntegerKey;
    }
}


//Department Item Holder
public class DepartmentItemHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
    private ImageView imageView = null;
    private TextView itemPriceTexView, itemNameTextView, itemWeightTextView, itemDiscountTextView, itemDiscountedPrice = null;
    private Spinner addToCartSpinner = null;
    private DepartmentItemDataObject departmentItemDataObject = null;

    public DepartmentItemHolder(View itemView) {
        super(itemView);
        this.imageView = (ImageView) itemView.findViewById(R.id.department_item_image);
        this.itemPriceTexView = (TextView) itemView.findViewById(R.id.department_item_price);
        this.itemNameTextView = (TextView) itemView.findViewById(R.id.department_item_name);
        this.itemWeightTextView = (TextView) itemView.findViewById(R.id.department_item_weight);
        this.itemDiscountTextView = (TextView) itemView.findViewById(R.id.department_item_discount);
        this.itemDiscountedPrice = (TextView) itemView.findViewById(R.id.department_item_discounted_price);
        this.addToCartSpinner = (Spinner) itemView.findViewById(R.id.department_add_to_cart_quantity);
        itemView.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        DepartmentItemClickProxy departmentItemClickProxy = new DepartmentItemClickProxy();
        departmentItemClickProxy.itemClicked(v, this.departmentItemDataObject);
    }

    public ImageView getImageView() {
        return this.imageView;
    }

    public TextView getItemPriceTexView() {
        return itemPriceTexView;
    }

    public TextView getItemNameTextView() {
        return itemNameTextView;
    }

    public TextView getItemWeightTextView() {
        return itemWeightTextView;
    }

    public TextView getItemDiscountTextView() {
        return itemDiscountTextView;
    }

    public TextView getItemDiscountedPrice() {
        return itemDiscountedPrice;
    }

    public void setViewListeners() {
        ItemAddToCartListener itemAddToCartListener = new ItemAddToCartListener(this.departmentItemDataObject);
        this.addToCartSpinner.setOnTouchListener(itemAddToCartListener);
        this.addToCartSpinner.setOnItemSelectedListener(itemAddToCartListener);
    }

    public Spinner getAddToCartSpinner() {
        return this.addToCartSpinner;
    }

    public DepartmentItemDataObject getDepartmentItemDataObject() {
        return this.departmentItemDataObject;
    }

    public void setDepartmentItemDataObject(DepartmentItemDataObject departmentItemDataObject) {
        this.departmentItemDataObject = departmentItemDataObject;
    }
}

//Function where Department Item Holder is added to map
    @Override
    public void onBindViewHolder(DepartmentItemHolder departmentItemHolder, int position) {
        departmentItemHolder.getItemNameTextView().setText(this.departmentItemDataObjects.get(position).getItemName());
        departmentItemHolder.getItemPriceTexView().setText(
                departmentItemHolder.getItemPriceTexView().getContext().getString(
                        R.string.currency,
                        this.departmentItemDataObjects.get(position).getItemPrice()
                )
        );
        if (0 < this.departmentItemDataObjects.get(position).getItemDiscount()) {
            departmentItemHolder.getItemDiscountTextView().setText(
                    departmentItemHolder.getItemDiscountTextView().getContext().getString(
                            R.string.discount_on_item,
                            this.departmentItemDataObjects.get(position).getItemDiscount()
                    )
            );
            departmentItemHolder.getItemDiscountedPrice().setText(
                    departmentItemHolder.getItemDiscountedPrice().getContext().getString(
                            R.string.currency,
                            ItemCheckoutUtility.getInstance().getDiscountedPrice(
                                    this.departmentItemDataObjects.get(position).getItemPrice(),
                                    this.departmentItemDataObjects.get(position).getItemDiscount()
                            )
                    )
            );
            Utilities.getInstance().strikeThroughText(departmentItemHolder.getItemPriceTexView());
        } else {
            departmentItemHolder.getItemDiscountTextView().setText(null);
            departmentItemHolder.getItemDiscountedPrice().setText(null);
            Utilities.getInstance().removeStrikeThroughFromText(departmentItemHolder.getItemPriceTexView());
        }
        departmentItemHolder.getItemWeightTextView().setText(this.departmentItemDataObjects.get(position).getItemWeightOrQuantity());
        departmentItemHolder.setDepartmentItemDataObject(this.departmentItemDataObjects.get(position));
        Glide.with(departmentItemHolder.getImageView().getContext())
                .load(Config.API_HOST + this.departmentItemDataObjects.get(position).getItemImageThumbnailUrl())
                .fitCenter()
                .crossFade()
                .into(departmentItemHolder.getImageView());
        departmentItemHolder.getAddToCartSpinner().setSelection(
                CartObserver.getCartObserverInstance().getQuantityToCheckoutFromMap(this.departmentItemDataObjects.get(position).getItemId()),
                false
        );
        departmentItemHolder.setViewListeners();
        CartObserver.getCartObserverInstance().addToDepartmentItemMap(departmentItemHolder);
    }

//HashMap Instantiation
private Map<CustomHashMapIntegerKey, List<DepartmentItemHolder>> departmentItemsMap = new HashMap<>();

//Addition of items to department items map
    public void addToDepartmentItemMap(DepartmentItemHolder departmentItemHolder) {
        if (this.appCompatActivity instanceof DepartmentPage || this.appCompatActivity instanceof SearchPage) {
            CustomHashMapIntegerKey customHashMapIntegerKey = departmentItemHolder.getDepartmentItemDataObject().getCustomHashMapIntegerKey();
            if (this.departmentItemsMap.containsKey(customHashMapIntegerKey)) {
                this.departmentItemsMap.get(customHashMapIntegerKey).add(departmentItemHolder);
            } else {
                List<DepartmentItemHolder> departmentItemHolders = new ArrayList<>();
                departmentItemHolders.add(departmentItemHolder);
                this.departmentItemsMap.put(customHashMapIntegerKey, departmentItemHolders);
            }
        }
    }