Java Stream API: Grouping Elements in a List

In Java, you can use the Stream API to perform various operations on a List, including grouping elements based on certain criteria. Here is an example of how you can use the Stream API to group elements in a List:

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

public class Main {
    public static void main(String[] args) {
        List<String> names = Arrays.asList('John', 'Jane', 'Adam', 'Eve', 'Alan', 'Alex');

        // Group names by their first letter
        Map<Character, List<String>> groupedNames = names.stream()
                .collect(Collectors.groupingBy(name -> name.charAt(0)));

        // Print the grouped names
        groupedNames.forEach((key, value) -> System.out.println(key + ': ' + value));
    }
}

Output:

A: [Adam, Alan, Alex]
J: [John, Jane]
E: [Eve]

In the above example, we create a List of names and use the stream() method to convert it into a Stream. Then, we use the collect() method along with Collectors.groupingBy() to group the names based on their first letter. Finally, we print the grouped names using the forEach() method on the resulting Map.