我正在为学校做作业，无法弄清楚为什么我的物品被我的购物车课程覆盖了。如果由我决定使用arraylist，但是赋值需要一个Items数组。
package jjobrien_assignement_4;
import java.util.Arrays;
import java.util.Scanner;
public class ShoppingCart extends Shopper{
private static final int DEFAULT_SIZE = 10;
String userName;
Item[] cart;
int itemCount = 0;
/**
* ShoppingCart default constructor
*/
public ShoppingCart(){
userName = "";
cart = new Item[DEFAULT_SIZE];
}
/**
* Shopping cart overloaded constructor
* @param aUserName
*/
public ShoppingCart(String aUserName){
userName = aUserName;
cart = new Item[DEFAULT_SIZE];
}
/**
* Adds a single item to the array cart[]
* @param cart
* @return
*/
public void addItem(Item theItem){
for(int i = 0; i < DEFAULT_SIZE; i++){
if(cart[i] == null){
System.out.print(i);
cart[i]= theItem;
itemCount += 1;
System.out.print(cart[i]);
break;
} //System.out.print(cart[i]);
}
}
public String removeItem(){
return "";
}
/**
*
* @param cleared
* @return cleared
* Will clear every object inside of the array cart[]
* by setting all valuse in the cart[] to null.
*/
public boolean clear(boolean cleared){
for(int i = 0; i < cart.length; i++){
cart[i] = null;
}
cleared = true;
itemCount = 0;
return cleared;
}
public String indexOf(){
return "";
}
/**
* Grabs single item from array to return to shopper
* @return
*/
public String getItem(){
String theItem = "";
for(int i = 0; i < itemCount; i++){
theItem = cart[i].getProductName();
}
return theItem;
}
public String showAll(String all){
for(int i = 0; i < itemCount; i++){
all += cart[i].getProductName() + " $"
+ cart[i].getPrice() + "\n";
}
return all;
}
/**
*
* @return
* Adds total cost and divides by item count to get avgCost
*/
public double showAverageCost(){
double avgCost = 0;
double totalCartCost = 0;
double singleItemCost = 0;
for(int i = 0; i < itemCount; i++){
singleItemCost = cart[i].getPrice();
totalCartCost = totalCartCost + singleItemCost;
}
avgCost = totalCartCost/itemCount;
return avgCost;
}
/**
*
* @param totalCartCost
* @return
* Calculates total cost by getting each price
* of all existing items in the array cart[].
*/
public double totalCost(double totalCartCost){
double singleItemCost = 0;
for(int i = 0; i < itemCount; i++){
singleItemCost = cart[i].getPrice();
totalCartCost = totalCartCost + singleItemCost;
}
return totalCartCost;
}
/**
* @return itemCount
* Counts how many items are in the shoppers cart
*/
public int countItems(){
int numOfItems = 0;
for(int i = 0; i < itemCount; i++){
numOfItems = numOfItems + 1;
}
return numOfItems;
}
}
}
{package jjobrien_assignement_4;
import java.util.Scanner;
import javax.swing.JOptionPane;
public class Shopper {
public final static String MENU = "\nSelect an option: \nType \"add\" to add an Item to the cart\n" +
"Type \"count\" to determine the total number of Items in the" +
"cart\n" +
"Type \"total cost\" to determine the total cost of Items in" +
"the cart\n" +
"Type \"show all\" to display the contents of the cart\n" +
"Type \"show average cost\" to display the average price of" +
"the contents of the cart\n" +
"Type \"cheapest\" to display the Item with the lowest price" +
"in the cart\n" +
"Type \"highest\" to display the Item with the highest price" +
"in the cart\n" +
"Type \"remove\" to remove a specific Item from the cart\n" +
"Type \"clear\" to remove all Items from the cart\n" +
"Type \"quit\" to exit the program: ";
public static void main (String [] args){
Scanner keyboard = new Scanner(System.in);
/*
cart[0] = new Item("Milk", 3.00);
cart[1] = new Item("Eggs", 4.25);
cart[2] = new Item("Bread", 2.50);
*/
boolean cleared = false;
boolean done = false;
double totalCartCost = 0.0;
String userName = "";
String userOption = "No option yet";
JOptionPane.showMessageDialog(null, "Welcome to the shopping cart!");
userName = JOptionPane.showInputDialog(null, "Please enter your name: ");
ShoppingCart newCart = new ShoppingCart(userName);
//While to display menu to customer and call methods based on user input
while(!done){
userOption = JOptionPane.showInputDialog(null, MENU);
if(userOption.equals("quit")){
if(quit(done) == true){
JOptionPane.showMessageDialog(null, "Thank you for using the Shopping Cart program!\n");
done = true;
}else if(quit(done) == false){
done = false;
}
}else if(userOption.equals("add")){
addItem(keyboard, newCart);
}else if(userOption.equals("count")){
}else if(userOption.equals("total cost")){
findTotalCost(newCart);
}else if(userOption.equals("show all")){
showAllItems(newCart);
}else if(userOption.equals("show average cost")){
showAverage(newCart);
}else if(userOption.equals("cheapest")){
//getCheapest();
}else if(userOption.equals("highest")){
//getHighest();
}else if(userOption.equals("remove")){
//remove();
}else if(userOption.equals("clear")){
clear(cleared, newCart);
}
}
}
/**
* Exits the program
*/
public static boolean quit(boolean isDone){
isDone = true;
return isDone;
}
/**
* Calls shopping cart class to add a single item to the array
* @param keyboard
* @param theCart
*/
public static void addItem(Scanner keyboard, ShoppingCart theCart){
String theItem = "";
String tempPrice = "";
Double thePrice = 0.0;
Item temp = null;
theItem = JOptionPane.showInputDialog(null, "Enter product name: ");
tempPrice = JOptionPane.showInputDialog(null, "Enter the price of " + theItem + ": ");
thePrice = Double.parseDouble(tempPrice);
temp = new Item(theItem, thePrice);
if(temp != null){
theCart.addItem(temp);
}
}
/**
* Will call ShoppingCart Clear Method
* @param cleared
* @param theCart
* @return
*/
public static boolean clear(boolean cleared, ShoppingCart theCart){
theCart.clear(cleared);
JOptionPane.showMessageDialog(null, "Your cart was cleared");
return cleared;
}
/**
* will call totalCost method from shopping cart class
* to add the total cost of all items stored in cart[]
* @param theCart
*/
public static void findTotalCost( ShoppingCart theCart){
double totalCost = 0;
JOptionPane.showMessageDialog(null, "Total cost: "
+ theCart.totalCost(totalCost));
}
/**
* Will print every item with their corresponding price
* in the cart[] array
*/
public static void showAllItems(ShoppingCart theCart){
String all = "";
JOptionPane.showMessageDialog(null, theCart.showAll(all));
}
/**
* calls shopping cart class to get average cost or all items
* in the current cart
*/
public static void showAverage(ShoppingCart theCart){
JOptionPane.showMessageDialog(null, theCart.showAverageCost());
}
}
}
{package jjobrien_assignement_4;
public class Item {
private static String productName;
private static double price;
public Item(){
productName = "No Name yet";
price = 0;
}
public Item(String aProductName, double aPrice){
setProductName(aProductName);
setPrice(aPrice);
}
public double getPrice(){
return price;
}
public String getProductName(){
return productName;
}
public double setPrice(double aPrice){
price = aPrice;
return aPrice;
}
public String setProductName(String aProductName){
productName = aProductName;
return aProductName;
}
public java.lang.String toString(){
String text = "";
text += productName.toString();
return text;
}
}
}
答案 0 :(得分：1)
您的Item类使用静态变量来存储其值。
静态变量是类级别 - 该变量只有一个实例，它由类的每个实例共享。
当您更改项目的值时（例如创建新项目时），您实际上正在更改静态变量 - 有效地为所有Item对象设置新值。
用标准成员变量替换静态变量应解决您的问题：
private String productName;
private double price;
请注意，Eclipse将使用以下语法自动生成构造函数和setter：
public void setSomething(String something) {
this.something = something;
}
如果您尝试以这种方式分配静态变量，Eclipse也应该给出警告（因为您在非静态上下文中使用静态变量。）
我不确定其他IDE - 但他们应该做类似的事情。