[英]Change value of arraylist field where object exists
我需要一些帮助,因为我被卡住了。 我有一个名为 orderList 的 ArrayList,类型为 ItemOrdered(int quantity,Item item)。 我想为 ArrayList 中存在给定项目的项目数量设置一个新值。 我尝试了一切,但没有奏效。
//place new order from buyer class
public void placeOrder(int quantity, Item item) {
//ItemOrdered newitemordered = new ItemOrdered(quantity,item );
ShoppingCart shoppingCart = new ShoppingCart();
shoppingCart.addItemOrdered(quantity,item);
}
//call placeOrder method
buyer.placeOrder(quantity,eshop.ItemListPen.get(x));
import java.util.ArrayList;
public class ShoppingCart {
public ArrayList<ItemOrdered> orderList = new ArrayList<ItemOrdered>();
public void addItemOrdered(int quantity,Item item) {
if(item.getStock() >= quantity && (!item.equals(orderList))){
ItemOrdered newitemordered = new ItemOrdered(quantity,item);
orderList.add(new ItemOrdered(quantity,item));
}else if(item.getStock() < quantity){
System.out.println("Sorry,this quantity is not available in stock.");
}else{
orderList.get(item).setQuantity(quantity);
System.out.println("nothing");
}
}
}
public class ItemOrdered {
static Item item;
private int quantity;
public ItemOrdered(int quantity, Item item){
this.quantity=quantity;
this.item=item;
}
public void setQuantity(int x){
quantity=quantity + x;
}
}
当库存大于或等于数量时,您似乎总是要进入if-else if-else
的if
块,因为第二个条件(.item.equals(orderList))
将为真。 这个条件应该检查列表是否包含项目,而不是列表和项目是否相等。 下一个难题是ItemOrdered
orderList
而不是Item
对象。 在这种情况下,简单地执行.orderList.contains(item)
也将始终返回 true。
您可以通过将包含Item
对象的列表作为ShoppingCart
的一部分来解决此问题,或者添加一个新方法来循环遍历orderList
并针对列表中的每个Item
检查item
。
选项 #1 - 向ShoppingCart
添加新的Item
对象列表:
public class ShoppingCart {
public ArrayList<ItemOrdered> orderList = new ArrayList<ItemOrdered>();
// This could also be public if you needed for some reason, but you could also achieve that by adding getter and setter methods
// depending on version of Java, you may need to include Item in <> when creating the new list: new ArrayList<Item>()
private ArrayList<Item> itemsInCart = new ArrayList<>();
public void addItemOrdered(int quantity,Item item) {
if(item.getStock() >= quantity && !itemsInCart.contains(item)){
ItemOrdered newitemordered = new ItemOrdered(quantity,item); // this could be removed, and you just create the new ItemOrdered within .add() on the next line
orderList.add(newitemordered);
itemsInCart.add(item); // have to update the new list of items
}else if(item.getStock() < quantity){
System.out.println("Sorry,this quantity is not available in stock.");
}else{
orderList.get(item).setQuantity(quantity);
System.out.println("nothing");
}
}
}
选项 #2 - 遍历 orderList:
public class ShoppingCart {
public ArrayList<ItemOrdered> orderList = new ArrayList<ItemOrdered>();
public void addItemOrdered(int quantity,Item item) {
if(item.getStock() >= quantity && !isItemInCart(item)){
orderList.add(new ItemOrdered(quantity,item));
}else if(item.getStock() < quantity){
System.out.println("Sorry,this quantity is not available in stock.");
}else{
orderList.get(item).setQuantity(quantity);
System.out.println("nothing");
}
}
private boolean isItemInCart(Item item){
for(ItemOrdered itemOrdered : orderList){
if(itemOrdered.getItem().equals(item)){
return true;
}
}
// Item is not in cart
return false;
}
}
public class ItemOrdered {
static Item item;
private int quantity;
public ItemOrdered(int quantity, Item item){
this.quantity=quantity;
this.item=item;
}
public void setQuantity(int x){
quantity=quantity + x;
}
public Item getItem(){
return this.item;
}
}
不同选项的注意事项:
orderList
非常大,循环可能会很昂贵(对于大多数实际情况来说可能不是什么大问题)Item
的.equals()
方法以准确定义要比较的内容以确定两个项目是否相等
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