Compiles, aber insgesamt wird nicht berechnet

Question

Anstelle der berechneten Ausgabe bekomme ich eine "Null" ohne die tatsächliche Gesamtausgabe, die ich suche. Ich denke, es ist, weil Artikel nicht richtig definiert ist. Mißachtung shop.txt hat es nicht auf mein Problem betrifft

package Shopping; 
import java.util.ArrayList; 
import java.util.Scanner; 
import java.io.File; 
import java.io.FileNotFoundException; 
import java.text.NumberFormat; 
public class Shop 
{ 
    public static void main(String[] args) 
    { 
     //I/O stream 

     String fileName = "shop.txt"; 
     Scanner inputStream = null; 
     System.out.println("The file " + fileName + 
       "\ncontains the following lines:\n"); 
     try 
     { 
      inputStream = new Scanner(new File(fileName)); 
     } 
     catch (FileNotFoundException e) 
     { 
      System.out.println("This is a shopping list " + 
        fileName); 
      System.exit(0); 
     } 
     while (inputStream.hasNextLine()) 
     { 
      String line = inputStream.nextLine(); 
      System.out.println(line); 
     } 
     inputStream.close(); 


     ArrayList<Item> Cart = new ArrayList<Item>(); 

     Item item; 
     String itemName; 
     double itemPrice; 
     int quantity; 
     double totalPrice = 0.0; 
     double sum = 0.0; 
     int priority; 

     Scanner scan = new Scanner(System.in); 
     String continueShopping = "y"; 
     do 
     { 
      System.out.print("Enter the name of the item: "); 
      itemName = scan.nextLine(); 
      System.out.print("Enter the unit price: "); 
      itemPrice = scan.nextDouble(); 
      System.out.print("Enter the quantity: "); 
      quantity = scan.nextInt(); 


      // create a new item and add it to the cart 

      item = new Item(itemName, itemPrice, quantity); 
      Cart.add(item); 

      for (int i = 0; i < Cart.size(); i++) 
      { 
       Item itm = Cart.get(i); 
       System.out.println(itm); 
      } 
      // Print out the results 

      System.out.print("Continue shopping (y/n)? "); 
      scan.nextLine(); 
      continueShopping = scan.nextLine(); 
     } 
     while (continueShopping.equals("y")); 
     for (int i = 0; i < Cart.size(); i++) 
     { 
      Item itm = Cart.get(i); 
      System.out.println(itm); 
      totalPrice = itm.getQuantity() * itm.getPrice(); 
      sum += totalPrice; 
     } 
     NumberFormat type = NumberFormat.getCurrencyInstance(); 
     System.out.println("The total price is: " + type.format(sum)); 
    } 
} 

Item-Klasse

package Shopping; 
import java.text.NumberFormat; 

public class Item 
{ 

    private String name; 
    private double price; 
    private int quantity; 


    public Item(String itemName, double itemPrice, int quantity2) 
    { 
    } 

    public void Item(String itemName, double itemPrice, int numPurchased) 
    { 
     name = itemName; 
     price = itemPrice; 
     quantity = numPurchased; 
    } 

    //Info about the item 

    public String toString() 
    { 
     NumberFormat type = NumberFormat.getCurrencyInstance(); 

     return (name + "\t" + type.format(price) + "\t" + quantity + "\t" 
       + type.format(price * quantity)); 
    } 

    //Retrieve the item price 

    public double getPrice() 
    { 
     return price; 
    } 

    //Retrieve item name 

    public String getName() 
    { 
     return name; 
    } 

    //Retrieve quantity 

    public int getQuantity() 
    { 
     return quantity; 
    } 
} 

Answer 1

Ihre Item Klasse hat einen leeren Konstruktor

public Item(String itemName, double itemPrice, int quantity2) { 
} 

und eine Methode namens Item

public void Item (String itemName, double itemPrice, int numPurchased) 
{ 
    name = itemName; 
    price = itemPrice; 
    quantity = numPurchased; 
} 

Entfernen Sie den leeren Konstruktor und entfernen Sie den Rückgabetyp void aus der Methode, um ihn in einen Konstruktor umzuwandeln.