Can you explain the concept of the functional programming paradigm?

The functional programming paradigm is based on using functions as the primary building blocks of a program. In it, functions are considered as pure mathematical functions — they have no side effects and always return the same result for the same inputs.

Main features:

• Immutability of data: data is not changed after creation; instead, new copies are created with modifications.
• Absence of side effects: functions do not alter the state outside themselves.
• Higher-order functions: functions can accept other functions as arguments and return them.
• Recursion instead of loops: recursion is often used for repetition.

Example in Java using lambda expressions and Stream API:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> doubled = numbers.stream()
    .map(n -> n * 2) // higher-order function map applies a function to each element
    .collect(Collectors.toList());

System.out.println(doubled); // [2, 4, 6, 8, 10]

Here, we do not modify the original list but create a new one by applying a function to each element.