java.lang.IllegalStateException : stream has already been operated upon or closed in Java while working with list

Question

这个问题已经有答案了:

Copy a stream to avoid "stream has already been operated upon or closed" (10 个回答)

已关闭 3 年前。

我有一个项目类和一个测试器类，用于订购项目和设置价格。我使用两种方法，并将流作为参数传递给方法。但执行时获取错误流已被操作或关闭。

项目类别:

public class Item {
int itemId;
String itemName;
ItemType itemType;
float weightInGrams;
float price;

public Item(int itemId, String itemName, ItemType itemType, float weightInGrams, float price) {
    this.itemId = itemId;
    this.itemName = itemName;
    this.itemType = itemType;
    this.weightInGrams = weightInGrams;
    this.price = price;
}

public int getItemId() {
    return itemId;
}

public void setItemId(int itemId) {
    this.itemId = itemId;
}

public String getItemName() {
    return itemName;
}

public void setItemName(String itemName) {
    this.itemName = itemName;
}

public ItemType getItemType() {
    return itemType;
}

public void setItemType(ItemType itemType) {
    this.itemType = itemType;
}

public float getWeightInGrams() {
    return weightInGrams;
}

public void setWeightInGrams(float weightInGrams) {
    this.weightInGrams = weightInGrams;
}

public float getPrice() {
    return price;
}

public void setPrice(float price) {
    this.price = price;
}

public static void filterItemsWeight(Stream<Item> items) {
    items.map(t-> t.getWeightInGrams())
        .sorted(Comparator.reverseOrder())
        .forEach(item-> System.out.println(item));
}
@Override
public String toString() {
    return "Item ID: "+this.getItemId()+" , Item Name : "+this.itemName+" , Item Type : "+this.itemType+
            " , Weight in grams : "+this.getWeightInGrams()+" , Price : "+this.getPrice();
}

public static void calculatePricePerItem(Stream<Item> itemsList) {
    Supplier<Stream<Item>> streamSupplier = ()-> itemsList;
    streamSupplier.get().filter(t-> t.getItemType().equals(ItemType.GOLD))
    .forEach(item->item.setPrice(item.getWeightInGrams()*2700));
    itemsList.forEach(t-> System.out.println(t));
    itemsList.filter(t-> t.getItemType().equals(ItemType.SILVER))
    .forEach(item->item.setPrice(item.getWeightInGrams()*34));
    itemsList.forEach(t-> System.out.println(t));

}

测试员类

public class Tester {
public static void main(String[] args) {
    Item it1 = new Item(10, "Ring", ItemType.GOLD, 23.3f, 40656.5f);
    Item it2 = new Item(11, "Necklace", ItemType.GOLD, 45.3f, 140656.5f);
    Item it3 = new Item(12, "Ring", ItemType.SILVER, 25.3f, 956.5f);
    Item it4 = new Item(13, "Coin", ItemType.GOLD, 20.3f, 37656.5f);
    Item it5 = new Item(14, "Bangle", ItemType.GOLD, 40f, 124200.5f);
    Item it6 = new Item(15, "Bangle", ItemType.GOLD, 45.3f, 140656.5f);
    List<Item> itemList = new ArrayList<>();
    itemList.add(it1);
    itemList.add(it2);
    itemList.add(it3);
    itemList.add(it4);
    itemList.add(it5);
    itemList.add(it6);
    Supplier<Stream<Item>> streamSupplier = ()-> itemList.stream();
    Item.filterItemsWeight(streamSupplier.get());
    Item.calculatePricePerItem(streamSupplier.get());

}

我尝试使用供应商流，但方法calculatePricePerItem仍然遇到相同的错误。您能帮忙解决这个问题吗？

Answer 1

之后

Supplier<Stream<Item>> streamSupplier = ()-> itemsList;
    streamSupplier.get().filter(t-> t.getItemType().equals(ItemType.GOLD))
    .forEach(item->item.setPrice(item.getWeightInGrams()*2700));

流已关闭。

所以下面这行 itemsList.forEach(t->System.out.println(t)

在已关闭的流上调用 foreach 终端操作。这是被禁止的。