Java 编程错误:java.util.ConcurrentModificationException [英] Java Programming Error: java.util.ConcurrentModificationException

问题描述

我正在编写一个程序作为初级 Java 学生教程的一部分.我有以下方法，每当我运行它时，它都会给我以下异常:

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)

这是 Warehouse 类中的方法本身:

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);
  }
}

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，因为循环不会遍历空的 ArrayList.

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.

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'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?

推荐答案

在迭代mCatalog 时不得修改它.您正在此循环中向其添加一个元素:

You must not modify mCatalog while you're iterating over it. You're adding an element to it in this loop:

for (MusicMedia m : myCatalog) { 
    if ( !m.getSKU().equals(product.getSKU()) ) {
            myCatalog.add(product);
    }
}

参见 ConcurrentModificationException 和 modCount 在 AbstractList.

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