How to Remove an Object from an ArrayList Using a For-Each Loop in Java?

How can I remove an object from an ArrayList while iterating over it using a for-each loop in Java?

ArrayList<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");

for(String item : list) {
    if(item.equals("B")) {
        list.remove(item); // This will cause ConcurrentModificationException
    }
}

Removing elements from a Java ArrayList while iterating over it using a for-each loop is problematic because it can lead to a ConcurrentModificationException. Instead, consider using an Iterator or filter the list based on certain conditions before deletion.

Iterator<String> iterator = list.iterator();

while(iterator.hasNext()) {
    String item = iterator.next();
    if(item.equals("B")) {
        iterator.remove(); // Safely removes the current element
    }
}

Causes

• Using for-each loop which modifies the ArrayList directly leads to ConcurrentModificationException.
• The iterator does not recognize the changes made to the collection during traversal.

Solutions

• Use an explicit Iterator to safely remove elements during iteration.
• Create a separate list to collect elements to be removed and delete them after the iteration.
• Utilize Java 8 Streams for filtering elements without modifying the original list.

Mistake: Attempting to remove an object from the ArrayList with a for-each loop directly.

Solution: Switch to using an explicit Iterator or store them for removal after the loop.

Mistake: Confusion between removing elements during iteration which causes exceptions.

Solution: Understand the flow of the for-each loop and the underlying collection modification rules.