Project Rental System Management - problem with rent method

Question

I'm creating a simple project which is used to manage library. I've a problem with a method rent to user. When user rents a book/magazine, the current quantity should reduce, but it's doesn't work. Where I did a mistake? Below is my code:

public class Library {

private final ArrayList<User> users = new ArrayList<>();
private final HashMap<Item, ItemDetails> items = new HashMap<>();

private boolean canBeRented(Item item) {
    return items.get(item).getCurrentQuantity() > 0;
}

private boolean canRent(Item item, User user) {
    return canBeRented(item) && user.canRent(item);
}
public boolean rentItemToUser(Item item, User user) {
    if (canRent(item, user)) {
        user.rent(item);
        items.get(item).decreaseCurrentQuantity();
        return true;
    }
    return false;
}

ItemDetails class:

public class ItemDetails {
private int totalQuantity;
private int currentQuantity;

public ItemDetails() {
    this(1, 1);
}

private ItemDetails(int totalQuantity, int currentQuantity) {
    this.totalQuantity = totalQuantity;
    this.currentQuantity = currentQuantity;
}

public int getTotalQuantity() {
    return totalQuantity;
}

public int getCurrentQuantity() {
    return currentQuantity;
}

public void decreaseCurrentQuantity() {
    this.currentQuantity = --currentQuantity;
}

void increaseQuantity() {
    this.currentQuantity++;
    this.totalQuantity++;
}

}