How to Efficiently Remove All Null Elements from an ArrayList or String Array?

What is the best way to remove all null elements from an ArrayList or a String array in Java?

// Sample ArrayList of Tourists
ArrayList<Tourist> tourists = new ArrayList<>();
tourists.add(new Tourist("Alice"));
tourists.add(null);
tourists.add(new Tourist("Bob"));
tourists.add(null);

// Using Java 8 to filter out null elements
ArrayList<Tourist> cleanedTourists = tourists.stream()
    .filter(Objects::nonNull)
    .collect(Collectors.toCollection(ArrayList::new));

Removing null elements from a collection such as an ArrayList or an array in Java can help streamline data processing and prevent NullPointerExceptions. Here are some efficient methods to achieve that.

// Improved approach using Java 8 Stream API
ArrayList<Tourist> cleanedTourists = tourists.stream()
    .filter(Objects::nonNull)
    .collect(Collectors.toCollection(ArrayList::new)); // Collecting non-null elements into a new ArrayList

Causes

• Null references can occur due to uninitialized objects or as a result of certain operations like filtering.
• Ignoring null values might lead to unexpected application behavior, especially when processing data.

Solutions

• Use Java 8 Stream API to filter out null values cleanly and concisely.
• Utilize an enhanced for-loop, but be cautious about performance issues with large data sets.
• Consider using an iterator for removing elements directly if working with an overhead from frequent updates.

Mistake: Using a standard loop to remove elements while iterating over the list.

Solution: Instead, create a new collection with filtered elements or use an iterator.

Mistake: Not considering the performance implications of frequent ArrayList resizing when removing elements.

Solution: Utilize a pre-sized ArrayList or filter and collect in one pass.