Trying to remove an object with list iterator

问题:

I'm trying to remove an object from a list using the list iterator. I've gone through the other solutions on the website and none have alleviated the error "Exception in thread "main" java.util.ConcurrentModificationException"

here is my code that is not executing :

void PatronReturn(String bookName) {
//       get to beginning
    while(listIterator.hasPrevious()) {
        listIterator.previous();
    }
    while(listIterator.hasNext()){
        Book b = listIterator.next();
    if (listIterator.next().getBookTitle().equals(bookName)) { 
        //listIterator.next();
        //listIterator.remove();
        books.remove(b);
        //listIterator.next(); //moves to next so iterator can remove previous ?
        //books.remove(listIterator.next());; // TODO see if this is correct

    }
    }

回答1:

1. Do not remove an item from a list directly. Use the remove() method in the iterator.

2. Your code is also flawed in that it assumes there are additional list items:

   while(listIterator.hasNext()){
       Book b = listIterator.next();
       if (listIterator.next().getBookTitle().equals(bookName)) { 
         // eek
   

   Here you call next() twice, yet you've only called hasNext once. Perhaps you meant:

   while(listIterator.hasNext()){
       Book b = listIterator.next();
       if (b.getBookTitle().equals(bookName)) { 
         // ...
   

3. Finally, you can replace:

   while(listIterator.hasPrevious()) {
       listIterator.previous();
   }
   

   with

   listIterator = books.listIterator();
   

回答2:

instead of books.remove(b)

use

listIterator.remove();

the reason is, that the iterator gives you the next() book, if you only remove the book from books, the iterator has the "removed" book still as next book.

it did not work in your code, because you called .next() twice, once for the book b and a second time when comparing the book title, with the next book.

回答3:

instead of books.remove(b)

try to use

   listIterator.remove();

回答4:

You can NOT remove an item from an ArrayList while iterating.

you can either :

• Use the remove() method of the ListIterator (at most once for each next())
• Use another List implementation, like CopyOnWriteArrayList, wich is garanteed never to throw an ConcurrentModificationException, but this is probably overkill in your case.

回答5:

You cannot remove an item whilst iterating a list, you should use .remove()

Also remove this:

while(listIterator.hasPrevious()) {
    listIterator.previous();
}

This is not neccesary

回答6:

{   Book toBeReaplced = null; Book tempBook = null;   
void PatronReturn(String bookName)           
{//       get to beginning
while(listIterator.hasPrevious()) {        listIterator.previous();
}
while(listIterator.hasNext()){
    Book tempBook = listIterator.next();
if (b.getBookTitle().equals(bookName)) { 
             toBeReaplced = tempBook;

}

listIterator.remove(bookToBeReplaced);
}

You can try the above code. I think it will able to solve your problem, that you have facing that java.util.ConcurrentModificationException" error. for more reference on the error please follow the link