Thread: Need advice in troubleshooting

I have trouble troubleshooting my project and sincerely hoping someone will be able to point out my coding mistakes. I was looking to add an Item in the application which I am working on my project.

I had attached my Item and ItemManager as well as the BidMenu. I did not attached my User and UserManager as they're both working perfectly, and so therefore I assumed either my ItemManager or my method to add item in BidMenu are wrongly-coded. Pls advice! Thank you.

public class Item{
 
	private String itemId;
	private String itemDescription;
	private User seller;
	private double minBid;
 
	public Item (String itemId, String itemDescription, User seller, double minBid){
		this.itemId = itemId;
		this.itemDescription = itemDescription;
		this.seller = seller;
		this.minBid = minBid;
	}
 
	public String getItemId(){
		return itemId;
	}
 
	public String getItemDescription(){
		return itemDescription;
	}
 
	public User getSeller(){
		return seller;
	}
 
	public double getMinBid(){
		return minBid;
	}
 
	public String toString(){
		return "The item " +itemDescription +" has been added with ID " +itemId;
	}
}

import java.util.*;
 
public class ItemManager{
 
	private UserManager userMgr;
	private ArrayList<Item> itemList;
 
	public ItemManager(){
		itemList = new ArrayList<Item>();
		itemList.add(new Item("I1","Java 6 book", userMgr.retrieveUser("plaura"),10.00));
		itemList.add(new Item("I2","Baby pram", userMgr.retrieveUser("johna"),20.00));
		itemList.add(new Item("I3","Water heater", userMgr.retrieveUser("mklee"),10.00));
		itemList.add(new Item("I4","Wedding gown", userMgr.retrieveUser("johna"),50.00));
	}
 
	public ArrayList<Item> retrieveAll(){
		return itemList;
	}
 
	public Item retrieveItem (String itemId) {
		for (int i=0; i<itemList.size(); i++){
			Item item = itemList.get(i);
			if (item.getItemId().equals(itemId)){
				return item;
			}
		}
		return null;
	}
 
	public void addItem (String itemId, String itemDescription, User seller, double minBid){
		Item item = new Item (itemId, itemDescription, seller, minBid);
		itemList.add(item);
	}
}

import java.util.*;
 
public class BidMenu{
 
	private ItemManager itemMgr;
	private UserManager userMgr;
	//private BidManager bidMgr;
	private Scanner sc;
 
	public BidMenu(){
		itemMgr = new ItemManager();
		userMgr = new UserManager();
		//bidMgr = new BidManager();
		sc = new Scanner(System.in);
	}
 
	public void display(){
		System.out.println("=== Merlion Xchange :: Main Menu ===");
		System.out.println("1. Add an Item");
		System.out.println("2. Bid for an Item");
		System.out.println("3. Add User");
		System.out.println("4. List all users");
		System.out.println("5. Close bid");
		System.out.println("6. View Report");
		System.out.println("7. Quit application");
		System.out.print("\nEnter your option > "); 
	}
 
	public void processAddItem(){
		System.out.println("\n=== Merlion Xchange :: Add Item ===");
		System.out.print("\nEnter Item Description > ");
		String itemDescription = sc.nextLine();
		ArrayList<User> userList = userMgr.retrieveAll();
		String userName = "";
		ArrayList<Item> itemList = itemMgr.retrieveAll();
 
		do {
			System.out.print("\nEnter seller username > ");
			userName = sc.nextLine();
			if (userMgr.retrieveUser(userName) == null){
				System.out.println("The username doesn't exist");
			}
		}while (userMgr.retrieveUser(userName) == null);
		User seller = userMgr.retrieveUser(userName);
 
		double minBid = 0;
		do {
		System.out.print("\nEnter minimum bid price > ");
		minBid = sc.nextDouble();
		if (minBid <= 0) {
			System.out.println("Kindly enter a bid price greater than $0");
		}
		} while (minBid <= 0);
 
		int listSize = itemList.size();
		int newId = itemList.size()+1;
		String itemId = "I"+newId;
		itemMgr.addItem(itemId, itemDescription, seller, minBid);
		/*for (int i= listSize; i<itemList.size(); i++){
			Item item = itemList.get(i);
			System.out.print(item.toString());
		}*/
		System.out.println(itemId);
	}
 
	public void processBidItem(){
		System.out.println("\n=== Merlion Xchange :: Bid for Item ===");
	}
 
	public void processAddUser(){
		System.out.println("\n=== Merlion Xchange :: Add User ===\n");
		String userName = "";
		double balance = 100.00;
		ArrayList<User> userList = userMgr.retrieveAll();
 
		do {
			System.out.print("Enter username for the new user > ");
			userName = sc.nextLine();
			if (userMgr.retrieveUser(userName) != null){
				System.out.println("The username already exists");
			}
		}while (userMgr.retrieveUser(userName) != null);
 
		System.out.println("\nThe following user has been added:\n");
		System.out.println("Username		Balance");
		System.out.println("====================================");
		int listSize = userList.size();
		userMgr.addUser(userName, balance);
		for (int i= listSize; i<userList.size(); i++){
			User user = userList.get(i);
			System.out.print(user.toString());
		}
		System.out.println();
	}
 
	public void processListAllUsers(){
		System.out.println("\n=== Merlion Xchange :: List all users ===");
		System.out.println("\nUsername		Balance");
		System.out.println("====================================");
		ArrayList<User> userList = userMgr.retrieveAll();
		for (int i=0; i<userList.size(); i++){
			User user = userList.get(i);
			System.out.print(user.toString());
		}
		System.out.println();
	}
 
	public void processCloseBid(){
		System.out.println("\n=== Merlion Xchange :: Close Bid ===");
	}
 
	public void processListHighestPoints(){
		System.out.println("\n=== Merlion Xchange :: View Report ===");
		System.out.println("\nUser(s) with the highest number of Xchange points:");
		System.out.println("\nUsername	Xchange Points");
		System.out.println("====================================");
	}
 
	public void readOption(){
		int option;
 
        do {
            display();
            option = sc.nextInt();
            sc.nextLine();  
 
            switch(option){
                case 1:processAddItem();                 
					   break;
                case 2:processBidItem();                  
					   break;
                case 3:processAddUser();
                       break;
                case 4:processListAllUsers();
                       break;
                case 5:processCloseBid();
                       break;
				case 6:processListHighestPoints();
                       break;
				case 7:System.out.println("\nThank you for using Merlion Xchange Bidding Items Application!\n");
                       break;
                default:System.out.println("Please enter a valid option (1 to 7)!");
            }
        } while(option != 7);
    }
}

Thank you, KevinWorkman! It is working now