Java peek vs map

Java peek vs map

In Java streams, peek() and map() are both intermediate operations that allow you to transform or interact with the elements of a stream. However, they serve slightly different purposes:

  1. map():

    • map() is an intermediate operation that transforms each element of the stream into a new element by applying a given function.
    • It returns a new stream with the transformed elements.
    • The original elements of the stream remain unchanged.
    • It's typically used when you want to perform a one-to-one transformation on each element of the stream.

    Example:

    List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5); List<Integer> squaredNumbers = numbers.stream() .map(x -> x * x) .collect(Collectors.toList());

  2. peek():

    • peek() is also an intermediate operation that allows you to perform some action or side effect on each element of the stream without changing the elements themselves.
    • It returns a new stream with the same elements as the original stream.
    • It's often used for debugging or logging purposes, or when you need to perform some action on each element while processing the stream.

    Example:

    List<String> fruits = Arrays.asList("apple", "banana", "cherry"); List<String> upperCaseFruits = fruits.stream() .map(String::toUpperCase) .peek(System.out::println) // Logging .collect(Collectors.toList());

So, the key difference is that map() transforms elements and returns a new stream with the transformed elements, while peek() allows you to perform side effects on elements without changing them and returns a new stream with the same elements.

When choosing between map() and peek(), consider your specific use case. If you need to transform elements, use map(). If you need to perform actions on elements while processing the stream, use peek(). However, be cautious when using peek() for side effects, as it can make the code less predictable and harder to reason about.

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