Is Removing Elements During a Java For-Each Loop Safe, and How Can It Be Done Correctly?

Removing Elements from a Collection During Iteration

In Java, altering a collection's content while iterating over it using a foreach loop can lead to unexpected behavior and exceptions. The question arises as to whether removing elements from the collection in this context is permissible.

Regarding the legality of removing elements in a foreach loop as in the example provided:

List<String> names = ....
for (String name : names) {
   // Do something
   names.remove(name).
}

The answer is yes, it is legal to remove elements within a foreach loop. However, it is essential to note that the collection's iterator may become invalid after removing an element, potentially leading to a ConcurrentModificationException.

Additionally, removing items that have not yet been iterated over (as in the second example) is not allowed. The iterator's implementation may or may not handle such scenarios gracefully. To avoid potential issues, ensure you iterate over all elements before attempting to remove any.

Using an Iterator for Safe Removal

To safely remove elements during iteration, it is recommended to use an explicit Iterator object. An iterator provides direct control over the removal process and ensures the collection remains valid throughout the loop.

List<String> names = ....
Iterator<String> i = names.iterator();
while (i.hasNext()) {
   String s = i.next(); // must be called before you can call i.remove()
   // Do something
   i.remove();
}

By using an iterator, you can safely remove elements without risking any exceptions or invalid collection states.

The above is the detailed content of Is Removing Elements During a Java For-Each Loop Safe, and How Can It Be Done Correctly?. For more information, please follow other related articles on the PHP Chinese website!