diff --git a/machine-learning/src/main/java/com/baeldung/ml/kmeans/Distance.java b/machine-learning/src/main/java/com/baeldung/ml/kmeans/Distance.java
index 37e1c8492e..88275d67bb 100644
--- a/machine-learning/src/main/java/com/baeldung/ml/kmeans/Distance.java
+++ b/machine-learning/src/main/java/com/baeldung/ml/kmeans/Distance.java
@@ -8,13 +8,13 @@ import java.util.Map;
  */
 public interface Distance {
 
-    /**
-     * Calculates the distance between two feature vectors.
-     *
-     * @param f1 The first set of features.
-     * @param f2 The second set of features.
-     * @return Calculated distance.
-     * @throws IllegalArgumentException If the given feature vectors are invalid.
-     */
-    double calculate(Map<String, Double> f1, Map<String, Double> f2);
+	/**
+	 * Calculates the distance between two feature vectors.
+	 *
+	 * @param f1 The first set of features.
+	 * @param f2 The second set of features.
+	 * @return Calculated distance.
+	 * @throws IllegalArgumentException If the given feature vectors are invalid.
+	 */
+	double calculate(Map<String, Double> f1, Map<String, Double> f2);
 }
diff --git a/machine-learning/src/main/java/com/baeldung/ml/kmeans/Errors.java b/machine-learning/src/main/java/com/baeldung/ml/kmeans/Errors.java
index 4b973c1146..25e70470c1 100644
--- a/machine-learning/src/main/java/com/baeldung/ml/kmeans/Errors.java
+++ b/machine-learning/src/main/java/com/baeldung/ml/kmeans/Errors.java
@@ -8,16 +8,16 @@ import java.util.Map;
  */
 public class Errors {
 
-    public static double sse(Map<Centroid, List<Record>> clustered, Distance distance) {
-        double sum = 0;
-        for (Map.Entry<Centroid, List<Record>> entry : clustered.entrySet()) {
-            Centroid centroid = entry.getKey();
-            for (Record record : entry.getValue()) {
-                double d = distance.calculate(centroid.getCoordinates(), record.getFeatures());
-                sum += Math.pow(d, 2);
-            }
-        }
+	public static double sse(Map<Centroid, List<Record>> clustered, Distance distance) {
+		double sum = 0;
+		for (Map.Entry<Centroid, List<Record>> entry : clustered.entrySet()) {
+			Centroid centroid = entry.getKey();
+			for (Record record : entry.getValue()) {
+				double d = distance.calculate(centroid.getCoordinates(), record.getFeatures());
+				sum += Math.pow(d, 2);
+			}
+		}
 
-        return sum;
-    }
+		return sum;
+	}
 }
diff --git a/machine-learning/src/main/java/com/baeldung/ml/kmeans/EuclideanDistance.java b/machine-learning/src/main/java/com/baeldung/ml/kmeans/EuclideanDistance.java
index 1946c508b4..7efc6e617b 100644
--- a/machine-learning/src/main/java/com/baeldung/ml/kmeans/EuclideanDistance.java
+++ b/machine-learning/src/main/java/com/baeldung/ml/kmeans/EuclideanDistance.java
@@ -7,19 +7,19 @@ import java.util.Map;
  */
 public class EuclideanDistance implements Distance {
 
-    @Override
-    public double calculate(Map<String, Double> f1, Map<String, Double> f2) {
-        if (f1 == null || f2 == null)
-            throw new IllegalArgumentException("Feature vectors can't be null");
+	@Override
+	public double calculate(Map<String, Double> f1, Map<String, Double> f2) {
+		if (f1 == null || f2 == null)
+			throw new IllegalArgumentException("Feature vectors can't be null");
 
-        double sum = 0;
-        for (String key : f1.keySet()) {
-            Double v1 = f1.get(key);
-            Double v2 = f2.get(key);
+		double sum = 0;
+		for (String key : f1.keySet()) {
+			Double v1 = f1.get(key);
+			Double v2 = f2.get(key);
 
-            if (v1 != null && v2 != null) sum += Math.pow(v1 - v2, 2);
-        }
+			if (v1 != null && v2 != null) sum += Math.pow(v1 - v2, 2);
+		}
 
-        return Math.sqrt(sum);
-    }
+		return Math.sqrt(sum);
+	}
 }
diff --git a/machine-learning/src/main/java/com/baeldung/ml/kmeans/LastFm.java b/machine-learning/src/main/java/com/baeldung/ml/kmeans/LastFm.java
index cdaf2170cd..0ff9d3cff4 100644
--- a/machine-learning/src/main/java/com/baeldung/ml/kmeans/LastFm.java
+++ b/machine-learning/src/main/java/com/baeldung/ml/kmeans/LastFm.java
@@ -13,40 +13,40 @@ import static java.util.stream.Collectors.toSet;
 
 public class LastFm {
 
-    private static OkHttpClient okHttp = new OkHttpClient.Builder()
-      .addInterceptor(new LastFmService.Authenticator("put your API key here"))
-      .build();
+	private static OkHttpClient okHttp = new OkHttpClient.Builder()
+	  .addInterceptor(new LastFmService.Authenticator("put your API key here"))
+	  .build();
 
-    private static Retrofit retrofit = new Retrofit.Builder().client(okHttp)
-      .addConverterFactory(JacksonConverterFactory.create())
-      .baseUrl("http://ws.audioscrobbler.com/")
-      .build();
+	private static Retrofit retrofit = new Retrofit.Builder().client(okHttp)
+	  .addConverterFactory(JacksonConverterFactory.create())
+	  .baseUrl("http://ws.audioscrobbler.com/")
+	  .build();
 
-    private static LastFmService lastFm = retrofit.create(LastFmService.class);
+	private static LastFmService lastFm = retrofit.create(LastFmService.class);
 
-    private static ObjectMapper mapper = new ObjectMapper();
+	private static ObjectMapper mapper = new ObjectMapper();
 
-    public static void main(String[] args) throws IOException {
+	public static void main(String[] args) throws IOException {
 		List<String> artists = getTop100Artists();
 		Set<String> tags = getTop100Tags();
 		List<Record> records = datasetWithTaggedArtists(artists, tags);
 
 		Map<Centroid, List<Record>> clusters = KMeans.fit(records, 7, new EuclideanDistance(), 1000);
-        // Print the cluster configuration
-        clusters.forEach((key, value) -> {
-            System.out.println("------------------------------ CLUSTER -----------------------------------");
+		// Print the cluster configuration
+		clusters.forEach((key, value) -> {
+			System.out.println("------------------------------ CLUSTER -----------------------------------");
 
-            System.out.println(sortedCentroid(key));
-            String members = String.join(", ", value.stream().map(Record::getDescription).collect(toSet()));
-            System.out.print(members);
+			System.out.println(sortedCentroid(key));
+			String members = String.join(", ", value.stream().map(Record::getDescription).collect(toSet()));
+			System.out.print(members);
 
-            System.out.println();
-            System.out.println();
-        });
+			System.out.println();
+			System.out.println();
+		});
 
 		Map<String, Object> json = convertToD3CompatibleMap(clusters);
 		System.out.println(mapper.writeValueAsString(json));
-    }
+	}
 
 	private static Map<String, Object> convertToD3CompatibleMap(Map<Centroid, List<Record>> clusters) {
 		Map<String, Object> json = new HashMap<>();
@@ -69,45 +69,45 @@ public class LastFm {
 	}
 
 	private static String dominantGenre(Centroid centroid) {
-        return centroid.getCoordinates().keySet().stream().limit(2).collect(Collectors.joining(", "));
-    }
+		return centroid.getCoordinates().keySet().stream().limit(2).collect(Collectors.joining(", "));
+	}
 
-    private static Centroid sortedCentroid(Centroid key) {
-        List<Map.Entry<String, Double>> entries = new ArrayList<>(key.getCoordinates().entrySet());
-        entries.sort((e1, e2) -> e2.getValue().compareTo(e1.getValue()));
+	private static Centroid sortedCentroid(Centroid key) {
+		List<Map.Entry<String, Double>> entries = new ArrayList<>(key.getCoordinates().entrySet());
+		entries.sort((e1, e2) -> e2.getValue().compareTo(e1.getValue()));
 
-        Map<String, Double> sorted = new LinkedHashMap<>();
-        for (Map.Entry<String, Double> entry : entries) {
-            sorted.put(entry.getKey(), entry.getValue());
-        }
+		Map<String, Double> sorted = new LinkedHashMap<>();
+		for (Map.Entry<String, Double> entry : entries) {
+			sorted.put(entry.getKey(), entry.getValue());
+		}
 
-        return new Centroid(sorted);
-    }
+		return new Centroid(sorted);
+	}
 
-    private static List<Record> datasetWithTaggedArtists(List<String> artists,
-                                                         Set<String> topTags) throws IOException {
-        List<Record> records = new ArrayList<>();
-        for (String artist : artists) {
-            Map<String, Double> tags = lastFm.topTagsFor(artist).execute().body().all();
+	private static List<Record> datasetWithTaggedArtists(List<String> artists,
+	  Set<String> topTags) throws IOException {
+		List<Record> records = new ArrayList<>();
+		for (String artist : artists) {
+			Map<String, Double> tags = lastFm.topTagsFor(artist).execute().body().all();
 
-            // Only keep popular tags.
-            tags.entrySet().removeIf(e -> !topTags.contains(e.getKey()));
+			// Only keep popular tags.
+			tags.entrySet().removeIf(e -> !topTags.contains(e.getKey()));
 
-            records.add(new Record(artist, tags));
-        }
-        return records;
-    }
+			records.add(new Record(artist, tags));
+		}
+		return records;
+	}
 
-    private static Set<String> getTop100Tags() throws IOException {
-        return lastFm.topTags().execute().body().all();
-    }
+	private static Set<String> getTop100Tags() throws IOException {
+		return lastFm.topTags().execute().body().all();
+	}
 
-    private static List<String> getTop100Artists() throws IOException {
-        List<String> artists = new ArrayList<>();
-        for (int i = 1; i <= 2; i++) {
-            artists.addAll(lastFm.topArtists(i).execute().body().all());
-        }
+	private static List<String> getTop100Artists() throws IOException {
+		List<String> artists = new ArrayList<>();
+		for (int i = 1; i <= 2; i++) {
+			artists.addAll(lastFm.topArtists(i).execute().body().all());
+		}
 
-        return artists;
-    }
+		return artists;
+	}
 }
diff --git a/machine-learning/src/main/java/com/baeldung/ml/kmeans/LastFmService.java b/machine-learning/src/main/java/com/baeldung/ml/kmeans/LastFmService.java
index 0cc8e9e285..4e2bf6bd92 100644
--- a/machine-learning/src/main/java/com/baeldung/ml/kmeans/LastFmService.java
+++ b/machine-learning/src/main/java/com/baeldung/ml/kmeans/LastFmService.java
@@ -8,6 +8,8 @@ import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
 
+import com.fasterxml.jackson.annotation.JsonAutoDetect;
+import com.fasterxml.jackson.annotation.JsonProperty;
 import okhttp3.HttpUrl;
 import okhttp3.Interceptor;
 import okhttp3.Request;
@@ -16,86 +18,89 @@ import retrofit2.Call;
 import retrofit2.http.GET;
 import retrofit2.http.Query;
 
+import static com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility.ANY;
 import static java.util.stream.Collectors.toList;
 
 public interface LastFmService {
 
-    @GET("/2.0/?method=chart.gettopartists&format=json&limit=50")
-    Call<Artists> topArtists(@Query("page") int page);
+	@GET("/2.0/?method=chart.gettopartists&format=json&limit=50")
+	Call<Artists> topArtists(@Query("page") int page);
 
-    @GET("/2.0/?method=artist.gettoptags&format=json&limit=20&autocorrect=1")
-    Call<Tags> topTagsFor(@Query("artist") String artist);
+	@GET("/2.0/?method=artist.gettoptags&format=json&limit=20&autocorrect=1")
+	Call<Tags> topTagsFor(@Query("artist") String artist);
 
-    @GET("/2.0/?method=chart.gettoptags&format=json&limit=100")
-    Call<TopTags> topTags();
+	@GET("/2.0/?method=chart.gettoptags&format=json&limit=100")
+	Call<TopTags> topTags();
 
-    /**
-     * HTTP interceptor to intercept all HTTP requests and add the API key to them.
-     */
-    class Authenticator implements Interceptor {
+	/**
+	 * HTTP interceptor to intercept all HTTP requests and add the API key to them.
+	 */
+	class Authenticator implements Interceptor {
 
-        private final String apiKey;
+		private final String apiKey;
 
-        Authenticator(String apiKey) {
-            this.apiKey = apiKey;
-        }
+		Authenticator(String apiKey) {
+			this.apiKey = apiKey;
+		}
 
-        @Override
-        public Response intercept(Chain chain) throws IOException {
-            HttpUrl url = chain.request().url().newBuilder().addQueryParameter("api_key", apiKey).build();
-            Request request = chain.request().newBuilder().url(url).build();
+		@Override
+		public Response intercept(Chain chain) throws IOException {
+			HttpUrl url = chain.request().url().newBuilder().addQueryParameter("api_key", apiKey).build();
+			Request request = chain.request().newBuilder().url(url).build();
 
-            return chain.proceed(request);
-        }
-    }
+			return chain.proceed(request);
+		}
+	}
 
-    @JsonAutoDetect(fieldVisibility = ANY)
-    class TopTags {
+	@JsonAutoDetect(fieldVisibility = ANY)
+	class TopTags {
 
-        private Map<String, Object> tags;
+		private Map<String, Object> tags;
 
-        @SuppressWarnings("unchecked")
-        public Set<String> all() {
-            List<Map<String, Object>> topTags = (List<Map<String, Object>>) tags.get("tag");
-            return topTags.stream().map(e -> ((String) e.get("name"))).collect(Collectors.toSet());
-        }
-    }
+		@SuppressWarnings("unchecked")
+		public Set<String> all() {
+			List<Map<String, Object>> topTags = (List<Map<String, Object>>) tags.get("tag");
+			return topTags.stream().map(e -> ((String) e.get("name"))).collect(Collectors.toSet());
+		}
+	}
 
-    @JsonAutoDetect(fieldVisibility = ANY)
-    class Tags {
+	@JsonAutoDetect(fieldVisibility = ANY)
+	class Tags {
 
-        @JsonProperty("toptags")
-        private Map<String, Object> topTags;
+		@JsonProperty("toptags")
+		private Map<String, Object> topTags;
 
-        @SuppressWarnings("unchecked")
-        public Map<String, Double> all() {
-            try {
-                Map<String, Double> all = new HashMap<>();
-                List<Map<String, Object>> tags = (List<Map<String, Object>>) topTags.get("tag");
-                for (Map<String, Object> tag : tags) {
-                    all.put(((String) tag.get("name")), ((Integer) tag.get("count")).doubleValue());
-                }
+		@SuppressWarnings("unchecked")
+		public Map<String, Double> all() {
+			try {
+				Map<String, Double> all = new HashMap<>();
+				List<Map<String, Object>> tags = (List<Map<String, Object>>) topTags.get("tag");
+				for (Map<String, Object> tag : tags) {
+					all.put(((String) tag.get("name")), ((Integer) tag.get("count")).doubleValue());
+				}
 
-                return all;
-            } catch (Exception e) {
-                return Collections.emptyMap();
-            }
-        }
-    }
+				return all;
+			}
+			catch (Exception e) {
+				return Collections.emptyMap();
+			}
+		}
+	}
 
-    @JsonAutoDetect(fieldVisibility = ANY)
-    class Artists {
+	@JsonAutoDetect(fieldVisibility = ANY)
+	class Artists {
 
-        private Map<String, Object> artists;
+		private Map<String, Object> artists;
 
-        @SuppressWarnings("unchecked")
-        public List<String> all() {
-            try {
-                List<Map<String, Object>> artists = (List<Map<String, Object>>) this.artists.get("artist");
-                return artists.stream().map(e -> ((String) e.get("name"))).collect(toList());
-            } catch (Exception e) {
-                return Collections.emptyList();
-            }
-        }
-    }
+		@SuppressWarnings("unchecked")
+		public List<String> all() {
+			try {
+				List<Map<String, Object>> artists = (List<Map<String, Object>>) this.artists.get("artist");
+				return artists.stream().map(e -> ((String) e.get("name"))).collect(toList());
+			}
+			catch (Exception e) {
+				return Collections.emptyList();
+			}
+		}
+	}
 }
diff --git a/machine-learning/src/main/java/com/baeldung/ml/kmeans/Record.java b/machine-learning/src/main/java/com/baeldung/ml/kmeans/Record.java
index 7208526136..0e936d49e6 100644
--- a/machine-learning/src/main/java/com/baeldung/ml/kmeans/Record.java
+++ b/machine-learning/src/main/java/com/baeldung/ml/kmeans/Record.java
@@ -9,52 +9,52 @@ import java.util.Objects;
  */
 public class Record {
 
-    /**
-     * The record description. For example, this can be the artist name for the famous musician
-     * example.
-     */
-    private final String description;
+	/**
+	 * The record description. For example, this can be the artist name for the famous musician
+	 * example.
+	 */
+	private final String description;
 
-    /**
-     * Encapsulates all attributes and their corresponding values, i.e. features.
-     */
-    private final Map<String, Double> features;
+	/**
+	 * Encapsulates all attributes and their corresponding values, i.e. features.
+	 */
+	private final Map<String, Double> features;
 
-    public Record(String description, Map<String, Double> features) {
-        this.description = description;
-        this.features = features;
-    }
+	public Record(String description, Map<String, Double> features) {
+		this.description = description;
+		this.features = features;
+	}
 
-    public Record(Map<String, Double> features) {
-        this("", features);
-    }
+	public Record(Map<String, Double> features) {
+		this("", features);
+	}
 
-    public String getDescription() {
-        return description;
-    }
+	public String getDescription() {
+		return description;
+	}
 
-    public Map<String, Double> getFeatures() {
-        return features;
-    }
+	public Map<String, Double> getFeatures() {
+		return features;
+	}
 
-    @Override
-    public String toString() {
-        String prefix = description == null || description.trim().isEmpty() ? "Record" : description;
+	@Override
+	public String toString() {
+		String prefix = description == null || description.trim().isEmpty() ? "Record" : description;
 
-        return prefix + ": " + features;
-    }
+		return prefix + ": " + features;
+	}
 
-    @Override
-    public boolean equals(Object o) {
-        if (this == o) return true;
-        if (o == null || getClass() != o.getClass()) return false;
-        Record record = (Record) o;
-        return Objects.equals(getDescription(), record.getDescription()) &&
-          Objects.equals(getFeatures(), record.getFeatures());
-    }
+	@Override
+	public boolean equals(Object o) {
+		if (this == o) return true;
+		if (o == null || getClass() != o.getClass()) return false;
+		Record record = (Record) o;
+		return Objects.equals(getDescription(), record.getDescription()) &&
+		  Objects.equals(getFeatures(), record.getFeatures());
+	}
 
-    @Override
-    public int hashCode() {
-        return Objects.hash(getDescription(), getFeatures());
-    }
+	@Override
+	public int hashCode() {
+		return Objects.hash(getDescription(), getFeatures());
+	}
 }