（这是文件的一部分，向您展示它的外观） 0001，Nikon D3300带AF-P DX 18-55mm VR数码单反，Nikon，396.95，
我想将这些对象添加到我前面提到的数组列表中，但这给了我这个错误：
线程“主”中的异常java.lang.NullPointerException 在programming2projectmain.Store.setArrProd（Programming2ProjectMain.java:462） 在programming2projectmain.Programming2ProjectMain.main（Programming2ProjectMain.java:69）
第69行： store.setArrProd（productObject）;
和商店类：
public void setArrProd(Products x){
(this is line 462) arrprod.add(x);
System.out.println(arrprod);
}
对于mu程序的第二个问题是，当我阅读产品信息（在for循环中）时，我也阅读了价格，因此我尝试打印它们，以便可以看到已存储的内容和未存储的内容。在循环中，它会按预期打印所有价格，但是一旦我知道了，它只会打印最后一个..这对我来说是个问题，因为我需要每种产品的价格来计算购物车中产品的总数，但我也不会不知道如何获取已添加商品的特定价格...
这是我的商店类别：
class Store{
private String name;
private ArrayList<Account> arracc;
private ArrayList<Products> arrprod;
public Store(){
}
public Store(String name){
this.name=name;
}
public ArrayList<Account> getArracc() {
return arracc;
}
public ArrayList<Products> getArrprod() {
return arrprod;
}
public int getAccountSize(){
return arracc.size();
}
public void setArrAcc(Account x){
arracc.add(x);
}
public void setArrProd(Products x){
arrprod.add(x);
System.out.println(arrprod);
}
public void addProduct(Products p){
arrprod.add(p);
}
public void deleteProduct(int id){
arrprod.remove(id);//id is the product index
}
public void setName(String name){
this.name=name;
}
public String getName(){
return name;
}
}
购物车类别：
class ShoppingCart{
ArrayList<OrderedItem> orderedItems=new ArrayList<OrderedItem>();
OrderedItem orders=new OrderedItem();
public ShoppingCart(OrderedItem x) {
orderedItems.add(x);
}
订购商品类：
class OrderedItem{
private Products productObject;
private int quantity;
ArrayList<ShoppingCart> cart=new ArrayList<ShoppingCart>();
public OrderedItem(){
productObject=new Products();
}
public OrderedItem(int quantity, Products productObject) {
this.quantity = quantity;
}
public void setQuantity(int q){
quantity=q;
}
public int getQuantity(){
return quantity;
}
public void setProductObject(Products productObject) {
this.productObject = productObject;
}
public Products getProductObject() {
return productObject;
}
}
产品类别：
class Products{
private String productID;
private String name;
private String supplier;
private double price;
public Products(){
}
public Products(String productID,String name,String supplier, double price){
this.productID=productID;
this.name=name;
this.supplier=supplier;
this.price=price;
}
public void setProductID(String ID){
productID=ID;
}
public void setName(String newName){
name=newName;
}
public void setSupplier(String newSupplier){
supplier=newSupplier;
}
public void setPrice(double newPrice){
price=newPrice;
}
public String getID(){
return productID;
}
public String getSupplier(){
return supplier;
}
public String getNAme(){
return name;
}
public double getPrice(){
return price;
}
public String toString(){
return" Product ID: "+productID+"\n -Product Name: "+name+"\n -Product Supplier: "+supplier+
"\n -Product Price: "+price+"\n ******************************************";
}
}
帐户类别：
class Account{
private String accountID;
private String username;
private String password;
private Customer robot;
private ShoppingCart relation;
private OrderedItem orders;
private Products PO=new Products();
public Account(){
}
public Account(String id,String userName,String password){
accountID=id;
username=userName;
this.password=password;
}
public void AddProducts(int q,String ID){
PO.setProductID(ID);
orders=new OrderedItem(q,PO);
}
public OrderedItem getProduct(){
return orders;
}
public void setAccountID(String accountID) {
this.accountID = accountID;
}
public void setUsername(String username) {
this.username = username;
}
public void setPassword(String password) {
this.password = password;
}
public String getAccountID() {
return accountID;
}
public String getUsername() {
return username;
}
public String getPassword() {
return password;
}
public String toString(){
return "Account ID: "+accountID+"\n Account username: "+username+"\n
Account Password: "+password+"\n "
+ "Customer Details for this Account: \n"+" -name:
"+robot.getName()+"\n -address: "+robot.getAddress()
+"\n -email: "+robot.getEmail()+"\n -phone number:
"+robot.getPhone()+"\n ****************************" ;
}
}
有一个客户类，它具有名称，地址，电话，电子邮件作为数据字段，以及它们的设置器和获取器。
主要：
public static void main(String[] args) {
Scanner input1=new Scanner(System.in);
int ans;
Store store = new Store("Camera Online Store");
Products productObject=new Products();
Account myAccount=new Account();
String[]splittedInfoProd;
String[]splittedInfoAcc;
int Q=0;
ArrayList<OrderedItem> cart;
boolean TF=false;
ArrayList<String>productsList=new ArrayList<String>();
// Read all products from the products file
File products = new File("Products.txt");
try(Scanner input = new Scanner(products);)
{
input.useDelimiter(",");
while(input.hasNextLine()){
productsList.add(input.nextLine());
}
input.close();
}catch(Exception ex){
System.out.println("Error in Products");
}
for(int i = 0; i< productsList.size(); i++) {
String account=productsList.get(i);
splittedInfoProd= account.split(",");
productObject.setProductID(splittedInfoProd[0]);
productObject.setName(splittedInfoProd[1]);
productObject.setSupplier(splittedInfoProd[2]);
productObject.setPrice(Double.valueOf(splittedInfoProd[3]));
productObject=new Products(productObject.getID(),productObject.getNAme(),productObject.getSupplier(),productObject.getPrice());
store.setArrProd(productObject);
} System.out.println(productObject.getPrice());
// Read all accounts from the account file
File customerFile = new File("Accounts.txt");
ArrayList<String>accountList=new ArrayList<String>();
try(Scanner input = new Scanner(customerFile);)
{
input.useDelimiter(",");
while(input.hasNextLine()){
accountList.add(input.nextLine());
);
} input.close();
}catch(Exception ex){
System.out.println("Error in Accounts");
}
for(int i = 0; i< accountList.size(); i++) {
String account=accountList.get(i);
splittedInfoAcc= account.split(",");
myAccount.setAccountID(splittedInfoAcc[0]);
myAccount.setUsername(splittedInfoAcc[1]);
myAccount.setPassword(splittedInfoAcc[2]);
myAccount=new Account(myAccount.getAccountID(),myAccount.getUsername(),myAccount.getPassword());
store.setArrAcc(myAccount);
}
System.out.println("^^^^^^ Welcome to our "+store.getName()+" ^^^^^");
System.out.println("*****************************************");
while(true)
{
System.out.println("Are you a customer or an admin?\n (1) for user \n (2) for admin\n (3) to exit");
Scanner sc = new Scanner (System.in);
int choice = sc.nextInt();
switch (choice) {
case 1: // customer mode
System.out.println("Enter your login information.");
System.out.print("Username:");
String username = sc.next();
System.out.print("Password:");
String password = sc.next();
int accountIndex=-1;
for (int i = 0; i < accountList.size(); i++) {
String[] userData = accountList.get(i).split(",");
if(userData[1].equals(username)&& userData[2].equals(password)){
accountIndex=i;
}
}
if(accountIndex<0)
System.out.println("Login Failed! Invalid Username and/or Password.\n");
else{
do
{
System.out.println("Choose the required operations from the list below:\n (1) Display all products \n (2) Add a product to your shopping cart by id \n (3) View the products in your shopping cart \n (4) Go to checkout\n (5) Go back to main menu");
choice = sc.nextInt();
sc.nextLine();
if(choice==1)
{
System.out.println("The list of available products: \n");
for (int i = 0; i < productsList.size(); i++) {
System.out.println(productsList.get(i));
}
}
else if (choice == 2)
{
System.out.println("Enter the id of the product: ");
String productID=input1.next();
for (int i = 0; i < productsList.size(); i++) {
String infoLine=productsList.get(i);
String[]CheckID=infoLine.split(",");
if((CheckID[0].equals(productID))){
TF=true;
break;
}
}if(TF){
System.out.println("Enter the product quantity: ");
Q=input1.nextInt();
myAccount.AddProducts(Q, productID);
System.out.println("The Product has been added to your cart");
}else{
System.out.println("Oops! incorrect product ID");
}
double Total=(Q*productObject.getPrice());
System.out.println(Total);
/*
add a product to shopping cart
....................
*/
}
else if (choice == 3)
{
//cart.add(myAccount.getProduct());
//System.out.println(cart);
/*
if( shoppingcart is Not empty )
{
display the products in the shopping cart
..............................
}
*/
}
else if (choice == 4) // checkout
{
/*
if( shoppingcart is Not empty )
{
print Receipt
..............................
Empty the shopping cart
..............................
}
*/
}
else if(choice == 5)
break;
System.out.println("Another user operation? (0) for yes | (1) for No.");
ans = sc.nextInt();
} while (ans==0);
}
break;
case 2:// Admin mode
do{
System.out.println("Choose the required operations from the list below:\n (1) Display all products \n (2) Display all accounts\n
(3) Add a product \n (4) Delete a product \n (5) Go back to main menu");
choice = sc.nextInt();
sc.nextLine();
if(choice==1) {
System.out.println("The list of available products:
\n");
for (int i = 0; i < productsList.size(); i++) {
System.out.println(productsList.get(i));
}
}
else if(choice == 2)
{
System.out.println("The list of accounts: \n");
for (int i = 0; i < accountList.size(); i++) {
System.out.println(accountList.get(i));
}
}
else if (choice == 3)
{
// read product details from the admin and add it to
the products array list within the store
System.out.println("Great! The product has been
added!");
}
else if(choice == 4)
{
/*
....................
*/
}
else if(choice == 5) break;
System.out.println("Another admin operation? (0) for yes| (1) for No");
ans = sc.nextInt();} while (ans==0);
break;
case 3:
System.out.println("Thanks for visiting our store!");
System.exit(0);
default:
System.out.println("Incorrect Entry! Try agian!");
break;
}
}
}
希望您能帮我提供我的代码，并先谢谢您！
答案 0 :(得分：1)
我认为问题在于列表未初始化。此外，通常对接口进行编码比对实现进行编码更好，因此以下更改可能会有所帮助：
class Store{
private String name;
// use interface and initialize;
private final List<Account> arracc = new ArrayList<>();
//same here
private final List<Products> arrprod = new ArrayList<>();
public Store(){
}
// return; note this exposes the internal storage, so may be incorrect
public List<Account> getArracc() {
return arracc;
}
// return the products; again, exposing internals and allows
// for anyone who calls getArrprod() to modify the list or the elements,
// which breaks encapsulation
public List<Products> getArrprod() {
return arrprod;
}
...
我认为第二个问题可以通过重构来解决。
private static loadProducts(Store store) {
ArrayList<String>productsList=new ArrayList<String>();
// Read all products from the products file
File products = new File("Products.txt");
try(Scanner input = new Scanner(products);)
{
input.useDelimiter(",");
while(input.hasNextLine()){
productsList.add(input.nextLine());
}
input.close();
}catch(Exception ex){
System.out.println("Error in Products");
}
for(int i = 0; i< productsList.size(); i++) {
String account=productsList.get(i);
splittedInfoProd= account.split(",");
String id = splittedInfoProd[0];
String name = splittedInfoProd[1];
String supplier = splittedInfoProd[2];
double price = Double.valueOf(splittedInfoProd[3]));
Products productObject = new Products (id, name, supplier, price);
store.setArrProd(productObject);
}
}
store将具有全部。
答案 1 :(得分：0)
第二期，
for(int i = 0; i< productsList.size(); i++) {
String account=productsList.get(i);
splittedInfoProd= account.split(",");
productObject.setProductID(splittedInfoProd[0]);
productObject.setName(splittedInfoProd[1]);
productObject.setSupplier(splittedInfoProd[2]);
productObject.setPrice(Double.valueOf(splittedInfoProd[3]));
productObject=new Products(productObject.getID(),productObject.getNAme(),productObject.getSupplier(),productObject.getPrice());
store.setArrProd(productObject);
} System.out.println(productObject.getPrice());
您的productObject在OrderedItem类中具有全局范围。因此，在for循环结束时，您的对象将存储最后一个值，并且当您要打印它时，它将打印最后一个值。所有价格，您应该迭代arraylist。
ArrayList<Products> list = store.getArrprod();
for(Products p : list){
System.out.println(p.getPrice());
}