How to Correctly Remove an Element from an ArrayList in Java?

What are the reasons I might be unintentionally removing the wrong element from an ArrayList in Java?

ArrayList<String> items = new ArrayList<>();
items.add("item1");
items.add("item2");
items.add("item3");

int indexToRemove = 1; // Example index to remove
items.remove(indexToRemove); // Removes "item2"

Removing an element from an ArrayList in Java can seem straightforward, but it may lead to unexpected behavior if not handled correctly. This guide will explore common issues and solutions for effectively managing elements in an ArrayList.

Iterator<String> iterator = items.iterator();
while(iterator.hasNext()) {
    String currentItem = iterator.next();
    if(currentItem.equals("item2")) {
        iterator.remove(); // Safely removes the item without throwing ConcurrentModificationException
    }
}

Causes

• Incorrect indices: Ensure that the index provided for removal is valid and within the current size of the list.
• Object comparison issues: When using the remove() method with objects, ensure that you are removing by the correct instance and not just by value, leading to confusion.
• Concurrent modification: Modifying an ArrayList while iterating over it can lead to unexpected results or exceptions.

Solutions

• Always verify the index before attempting to remove an element. Use size() method to ensure the index is within range.
• When removing an object, use the correct instance reference to avoid confusion; consider using .equals() method appropriately.
• If necessary, use Iterators for safe removal during iteration. This prevents ConcurrentModificationException.

Mistake: Assuming the index is always valid which results in IndexOutOfBoundsException.

Solution: Check the size of the ArrayList with size() before performing the removal using an index.

Mistake: Not using the correct instance while removing objects which could lead to removing the wrong element by value instead of by reference.

Solution: Ensure the object being removed matches the intended instance, or use overloaded remove() methods appropriately.