Explain the purpose of the distinct() method and in what cases it is used when working with collections.

The distinct() method in Java is used to remove duplicates from a data stream (Stream). It returns a new stream containing only unique elements, preserving the order of their first appearance.

Most often, distinct() is applied when you need to obtain a set of unique values from a collection or the result of computations, for example, to remove repeated elements before further processing.

Example:

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class DistinctExample {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 2, 3, 4, 4, 5);
        List<Integer> uniqueNumbers = numbers.stream()
                                           .distinct()
                                           .collect(Collectors.toList());
        System.out.println(uniqueNumbers); // [1, 2, 3, 4, 5]
    }
}

Thus, distinct() helps to eliminate duplicates and obtain a clean dataset.