Java 编程错误：java.util.ConcurrentModificationException
我正在编写一个程序作为 Java 初学者教程的一部分。我有以下方法，每当我运行它时，它都会给出以下异常：
java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
at java.util.AbstractList$Itr.next(AbstractList.java:343)
at Warehouse.receive(Warehouse.java:48)
at MainClass.main(MainClass.java:13)
这是方法本身，在 Warehouse 类中：
public void receive(MusicMedia product, int quantity) {
if ( myCatalog.size() != 0) { // Checks if the catalog is empty
// if the catalog is NOT empty, it will run through looking to find
// similar products and add the new product if there are none
for (MusicMedia m : myCatalog) {
if ( !m.getSKU().equals(product.getSKU()) ) {
myCatalog.add(product);
}
}
} else { // if the catalog is empty, just add the product
myCatalog.add(product);
}
}
问题似乎出在 if else 语句上。如果我不包含 if else，则程序将运行，尽管它无法正常工作，因为循环不会迭代空的 ArrayList。
我尝试添加一个产品只是为了防止它在代码的其他部分为空，但它仍然给我同样的错误。有什么想法吗？
I'm writing a program as part of tutorial for a beginner Java student. I have the following method and whenever I run it, it gives me the following exception:
java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
at java.util.AbstractList$Itr.next(AbstractList.java:343)
at Warehouse.receive(Warehouse.java:48)
at MainClass.main(MainClass.java:13)
Here's the method itself, within the class Warehouse:
public void receive(MusicMedia product, int quantity) {
if ( myCatalog.size() != 0) { // Checks if the catalog is empty
// if the catalog is NOT empty, it will run through looking to find
// similar products and add the new product if there are none
for (MusicMedia m : myCatalog) {
if ( !m.getSKU().equals(product.getSKU()) ) {
myCatalog.add(product);
}
}
} else { // if the catalog is empty, just add the product
myCatalog.add(product);
}
}
The problem seems to be with the if else statement. If I don't include the if else, then the program will run, although it won't work properly because the loop won't iterate through an empty ArrayList.
I've tried adding a product just to keep it from being empty in other parts of the code, but it still gives me the same error. Any ideas?
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您无法迭代要添加内容的同一个列表。单独列出要添加的内容，然后将它们全部添加到最后。
You can't be iterating through the same list you're going to add things to. Keep a separate list of the things you're going to add, then add them all at the end.
在迭代时不得修改
mCatalog。您在此循环中向其中添加一个元素：请参阅 ConcurrentModificationException 和 modCount在 摘要列表。
You must not modify
mCatalogwhile you're iterating over it. You're adding an element to it in this loop:See ConcurrentModificationException and modCount in AbstractList.