What are the differences between using Stream API and regular collections for data processing in Java?

Stream API in Java provides a declarative way to process collections, allowing for more readable and concise code. Main differences from regular collections:

• Lazy evaluation: Stream operations (except terminal ones) are performed lazily, meaning they are computed only when necessary.
• Parallelism: Stream API easily allows parallel operations, which is difficult to implement with regular collections.
• Functional style: Stream uses lambda expressions and functional interfaces, simplifying transformation chains.
• Immutability: Stream does not modify the original collection but returns a new data stream.

Example of using Stream for filtering and transforming a list:

List<String> names = Arrays.asList("Anna", "Bob", "Charlie", "David");
List<String> filtered = names.stream()
    .filter(name -> name.length() > 3)
    .map(String::toUpperCase)
    .collect(Collectors.toList());

Unlike this, regular collections require explicit loops and conditions for similar operations.