Example: SortArrayByFrequencyStreams in Java

// SortArrayByFrequencyStreams
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

// Main class containing the entry point of the program
public class Main {
    public static void main(String[] args) {
        int[] arr = {2, 3, 2, 4, 5, 12, 2, 3, 3, 3, 12};
        System.out.println("Original Array: " + Arrays.toString(arr));

        // Step 1: Count frequencies using Streams
        Map<Integer, Long> frequencyMap = Arrays.stream(arr)
                                              .boxed() // Convert int[] to Stream<Integer>
                                              .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));

        // Step 2: Create a list of elements from the original array
        List<Integer> list = Arrays.stream(arr).boxed().collect(Collectors.toList());

        // Step 3: Sort the list using a custom comparator that utilizes the frequency map
        list.sort(Comparator
            .<Integer>comparing(num -> frequencyMap.get(num), Comparator.reverseOrder()) // Sort by frequency decreasing
            .thenComparing(Function.identity()) // Then by natural order (ascending value) if frequencies are equal
        );

        System.out.println("Sorted by Frequency (Decreasing) using Streams: " + list);
    }
}