如何将新对象添加到ArrayList？

Question

I'm trying to add a new object to an ArrayList. Each Item object will have 3 attributes:

1. itemNum
2. info
3. cost

I also have 3 classes:

1. Item class defines the single items stored in the catalog.
2. Catalog class maintains the list of the Item objects.
3. Client class w/main method.

I have the sets and gets in Item class and I have the ArrayList in Catalog. In Client, I will have options to add, remove, or edit the objects. How do I correctly add a new Item object to the ArrayList?

I get the Item class to compile fine, but the Catalog and Client classes are not compiling. Here's the error I get with Catalog class:

Catalog.java:35: error: no suitable method found for add(int,String,double)listOfObjects.add(newItemId, newDescription, newCost); 
 method ArrayList.add(int,Item) is not applicable
 (actual and formal argument lists differ in length)
 method ArrayList.add(Item) is not applicable
(actual and formal argument lists differ in length)

Below is code for Item class

 Public class Item 
 {
  private int itemNum;
  private String info;
  private double cost;   

  public Item()
  {   //start constructor
     itemNum = 0;   //default values
     info = "x";
     cost = 0;
  }   //end constructor

  public CatalogItem(int newItemNum, String newInfo, double newCost)
  {   //start overload constructor
     this.itemNum = newItemNum;
     this.info = newInfo;
     this.cost = newCost;
  }   //end overload constructor

below are the set/gets for itemNum

     public int getItemNum()
     {   //start itemNum accessor
     return itemNum;
     }   //end getItemNum

  public void setItemNum(int newItemNum)
  {   //start itemNum mutator
     this.itemNum = newItemNum;
  }   //end setItemNum
 }   //end Item class

//below is my Catalog Class

 import java.util.*;

    public class Catalog
     {   //start class
      private ArrayList<CatalogItem> listOfObjects = new ArrayList<CatalogItem>(100);   //creates ArrayList
     Item newItem = new Item(newItemNum, newInfo, newCost);   //instantiates Item class

  /*
  public Catalog()
  {   //start constructor

  }   //end constructor     
  */

 public void add(CatalogItem newItem)   //method adds a new Item object to the array list
  {   //start add
     listOfObjects.add(newItem);

  }   //end add  

  public void add(int itemNum, String info, double cost)   //accepts parameters from main method to add to new object
  {   //start add
     int newItemNum = itemNum;
     String newInfo = info;
     double newCost = cost;

    newItem.setItemNum(newItemNum);
    newItem.setInfo(newInfo);
     newItem.setCost(newCost);

     listOfObjects.add(newItemNum, newInfo, newCost);

  }   //end add
 }     //end class

below is Client class. It receives input from the user regarding the itemNum, info, and cost

 import java.util.*;   //allows use of Scanner class

public class Client
{   //start client class

  public static void main(String[] args)
  {   //start main
     Catalog serv = new Catalog();   //creates instance of Catalog class
     Scanner scan = new Scanner(System.in);   //creates instance of Scanner class called scan

  public void add(int itemNum, String info, double cost)   //accepts parameters from main method to add to new object
  {   //start add
     int newItemNum = itemNum;
     String newInfo = info;
     double newCost = cost;

     newItem.setItemNum(newItemNum);
     newItem.setInfo(newInfo);
     newItem.setCost(newCost);

     listOfObjects.add(newItemNum, newInfo, newCost);   //adds the object to the ArrayList

  }   //end add
 }

Any help would be greatly appreciated.

Answer 1

You have some errors...

In your class Catalog, this line is not correct:

listOfObjects.add(newItemNum, newInfo, newCost);   //adds the object to the ArrayList

you must do:

CatalogItem cat = new CatalogItem(newItemNum, newInfo, newCost);
listOfObjects.add(cat);   //adds the object to the ArrayList

And in your class Client, you have not reference to newItem nor listOfObjects, so you cannot use them in that class. If you want to add elements to listOfObjects from your Client's main method, you can do something like this:

public class Client {
    public static void main(String[] args) {   //start main
        Catalog serv = new Catalog();
        ......
        serv.add(1, "", 1.0d);
    }
}