错误声明 byte[] 数组副本的 ArrayList 返回了欺骗性错误消息，说要使用迭代器

Question

I am trying to copy an ArrayList of byte[] array within a builder constructor. I want to copy arrayLst1 to arrayLst2. I tried doing it with this code:

builder.arrayLst2.forEach(item->this.arrayLst1.add(item)); 

but I got the following error:

Exception in thread "main" java.util.ConcurrentModificationException

So Google lead me to Iterators here , here and here so I tried this code (and other variations).

    for (Iterator itr = builder.arrayLst1.iterator(); itr.hasNext();) {
        this.arrayLst2.add(itr.next());
    }

The second line gives the error message "no suitable method found for add method."

I have tried along the lines of:

Iterator itr = this.arrayLst.iterator();        
builder.arrayLst2.forEach(item->itr.next()  );

but I can't figure out how to step through the first array1 and use iterator to add/copy to array2.

How do I clone one ArrayList byte[] to another? I am sure there must be an easy solution but I can't find it.

Edit: The declaration error effectively meant that the arraylist wasn't declared. Rather than say this, the compiler error message pointed to needing to use an iterator.

Answer 1

this.arrayLst1 = new ArrayList<>(builder.arrayLst2);

or

this.arrayLst1 = new ArrayList<>();
this.arrayLst1.addAll(builder.arrayLst2);

Answer 2

Credit to this answer belongs to #Zaki Anwar Hamdani. I made an error in the declaration.

The following declaration works.

        this.flagImgs = new ArrayList <>( this.flagImageFilenames.size());
        builder.flagImgs.forEach(item->this.flagImgs.add(item)); 

The thing that stumped me was that the error messages did not hint at a problem with the declaration. The reference to Iterators sent me on a wild goose chase to nowhere.