Fixed a lot of possible issues raised by a code inspection

app/src/main/java/com/cappielloantonio/play/subsonic/Subsonic.java

@@ -20,8 +20,8 @@ public class Subsonic {
 
     private final Context context;
 
-    private Version apiVersion = API_MAX_VERSION;
-    private SubsonicPreferences preferences;
+    private final Version apiVersion = API_MAX_VERSION;
+    private final SubsonicPreferences preferences;
 
     private SystemClient systemClient;
     private BrowsingClient browsingClient;

app/src/main/java/com/cappielloantonio/play/subsonic/base/Version.java

@@ -1,5 +1,7 @@
 package com.cappielloantonio.play.subsonic.base;
 
+import androidx.annotation.NonNull;
+
 public class Version implements Comparable<Version> {
 
     private static final String VERSION_PATTERN = "[0-9]+(\\.[0-9]+)*";
@@ -49,6 +51,7 @@ public class Version implements Comparable<Version> {
         return 0;
     }
 
+    @NonNull
     @Override
     public String toString() {
         return versionString;

app/src/main/java/com/cappielloantonio/play/subsonic/models/AlbumList.java

@@ -28,7 +28,7 @@ public class AlbumList {
      */
     public List<Child> getAlbums() {
         if (albums == null) {
-            albums = new ArrayList<Child>();
+            albums = new ArrayList<>();
         }
         return this.albums;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/ArtistInfo.java

@@ -28,7 +28,7 @@ public class ArtistInfo extends ArtistInfoBase {
      */
     public List<Artist> getSimilarArtists() {
         if (similarArtists == null) {
-            similarArtists = new ArrayList<Artist>();
+            similarArtists = new ArrayList<>();
         }
         return this.similarArtists;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/ArtistInfo2.java

@@ -1,7 +1,6 @@
 package com.cappielloantonio.play.subsonic.models;
 
 import com.tickaroo.tikxml.annotation.Element;
-import com.tickaroo.tikxml.annotation.ElementNameMatcher;
 import com.tickaroo.tikxml.annotation.Xml;
 
 import java.util.ArrayList;

app/src/main/java/com/cappielloantonio/play/subsonic/models/Bookmarks.java

@@ -28,7 +28,7 @@ public class Bookmarks {
      */
     public List<Bookmark> getBookmarks() {
         if (bookmarks == null) {
-            bookmarks = new ArrayList<Bookmark>();
+            bookmarks = new ArrayList<>();
         }
         return this.bookmarks;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/ChatMessages.java

@@ -28,7 +28,7 @@ public class ChatMessages {
      */
     public List<ChatMessage> getChatMessages() {
         if (chatMessages == null) {
-            chatMessages = new ArrayList<ChatMessage>();
+            chatMessages = new ArrayList<>();
         }
         return this.chatMessages;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/Directory.java

@@ -36,7 +36,7 @@ public class Directory {
      */
     public List<Child> getchildren() {
         if (children == null) {
-            children = new ArrayList<Child>();
+            children = new ArrayList<>();
         }
         return this.children;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/ErrorCode.java

@@ -11,7 +11,7 @@ public class ErrorCode {
     public static int TRIAL_PERIOD_OVER = 60;
     public static int DATA_NOT_FOUND = 70;
 
-    private int value;
+    private final int value;
 
     public ErrorCode(int value) {
         this.value = value;

app/src/main/java/com/cappielloantonio/play/subsonic/models/Index.java

@@ -29,7 +29,7 @@ public class Index {
      */
     public List<Artist> getArtists() {
         if (artists == null) {
-            artists = new ArrayList<Artist>();
+            artists = new ArrayList<>();
         }
         return this.artists;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/Indexes.java

@@ -32,7 +32,7 @@ public class Indexes {
      */
     public List<Artist> getShortcuts() {
         if (shortcuts == null) {
-            shortcuts = new ArrayList<Artist>();
+            shortcuts = new ArrayList<>();
         }
         return this.shortcuts;
     }
@@ -59,7 +59,7 @@ public class Indexes {
      */
     public List<Index> getIndices() {
         if (indices == null) {
-            indices = new ArrayList<Index>();
+            indices = new ArrayList<>();
         }
         return this.indices;
     }
@@ -86,7 +86,7 @@ public class Indexes {
      */
     public List<Child> getchildren() {
         if (children == null) {
-            children = new ArrayList<Child>();
+            children = new ArrayList<>();
         }
         return this.children;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/InternetRadioStations.java

@@ -28,7 +28,7 @@ public class InternetRadioStations {
      */
     public List<InternetRadioStation> getInternetRadioStations() {
         if (internetRadioStations == null) {
-            internetRadioStations = new ArrayList<InternetRadioStation>();
+            internetRadioStations = new ArrayList<>();
         }
         return this.internetRadioStations;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/JukeboxPlaylist.java

@@ -28,7 +28,7 @@ public class JukeboxPlaylist extends JukeboxStatus {
      */
     public List<Child> getEntries() {
         if (entries == null) {
-            entries = new ArrayList<Child>();
+            entries = new ArrayList<>();
         }
         return this.entries;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/NewestPodcasts.java

@@ -28,7 +28,7 @@ public class NewestPodcasts {
      */
     public List<PodcastEpisode> getEpisodes() {
         if (episodes == null) {
-            episodes = new ArrayList<PodcastEpisode>();
+            episodes = new ArrayList<>();
         }
         return this.episodes;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/NowPlaying.java

@@ -28,7 +28,7 @@ public class NowPlaying {
      */
     public List<NowPlayingEntry> getEntries() {
         if (entries == null) {
-            entries = new ArrayList<NowPlayingEntry>();
+            entries = new ArrayList<>();
         }
         return this.entries;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/PlayQueue.java

@@ -34,7 +34,7 @@ public class PlayQueue {
      */
     public List<Child> getEntries() {
         if (entries == null) {
-            entries = new ArrayList<Child>();
+            entries = new ArrayList<>();
         }
         return this.entries;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/PodcastChannel.java

@@ -36,7 +36,7 @@ public class PodcastChannel {
      */
     public List<PodcastEpisode> getEpisodes() {
         if (episodes == null) {
-            episodes = new ArrayList<PodcastEpisode>();
+            episodes = new ArrayList<>();
         }
         return this.episodes;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/Podcasts.java

@@ -28,7 +28,7 @@ public class Podcasts {
      */
     public List<PodcastChannel> getChannels() {
         if (channels == null) {
-            channels = new ArrayList<PodcastChannel>();
+            channels = new ArrayList<>();
         }
         return this.channels;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/ResponseStatus.java

@@ -8,7 +8,7 @@ public class ResponseStatus {
     public static String OK = "ok";
     public static String FAILED = "failed";
 
-    private String value;
+    private final String value;
 
     public ResponseStatus(@Attribute String value) {
         this.value = value;

app/src/main/java/com/cappielloantonio/play/subsonic/models/SearchResult.java

@@ -30,7 +30,7 @@ public class SearchResult {
      */
     public List<Child> getMatches() {
         if (matches == null) {
-            matches = new ArrayList<Child>();
+            matches = new ArrayList<>();
         }
         return this.matches;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/Share.java

@@ -37,7 +37,7 @@ public class Share {
      */
     public List<Child> getEntries() {
         if (entries == null) {
-            entries = new ArrayList<Child>();
+            entries = new ArrayList<>();
         }
         return this.entries;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/Shares.java

@@ -28,7 +28,7 @@ public class Shares {
      */
     public List<Share> getShares() {
         if (shares == null) {
-            shares = new ArrayList<Share>();
+            shares = new ArrayList<>();
         }
         return this.shares;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/SimilarArtistID3.java

@@ -2,9 +2,6 @@ package com.cappielloantonio.play.subsonic.models;
 
 import com.tickaroo.tikxml.annotation.Attribute;
 import com.tickaroo.tikxml.annotation.Xml;
-import com.tickaroo.tikxml.converters.date.rfc3339.DateRfc3339TypeConverter;
-
-import java.util.Date;
 
 @Xml(name = "similarArtist")
 public class SimilarArtistID3 {

app/src/main/java/com/cappielloantonio/play/subsonic/models/SimilarSongs.java

@@ -28,7 +28,7 @@ public class SimilarSongs {
      */
     public List<Child> getSongs() {
         if (songs == null) {
-            songs = new ArrayList<Child>();
+            songs = new ArrayList<>();
         }
         return this.songs;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/Starred.java

@@ -30,7 +30,7 @@ public class Starred {
      */
     public List<Artist> getArtists() {
         if (artists == null) {
-            artists = new ArrayList<Artist>();
+            artists = new ArrayList<>();
         }
         return this.artists;
     }
@@ -57,7 +57,7 @@ public class Starred {
      */
     public List<Child> getAlbums() {
         if (albums == null) {
-            albums = new ArrayList<Child>();
+            albums = new ArrayList<>();
         }
         return this.albums;
     }
@@ -84,7 +84,7 @@ public class Starred {
      */
     public List<Child> getSongs() {
         if (songs == null) {
-            songs = new ArrayList<Child>();
+            songs = new ArrayList<>();
         }
         return this.songs;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/User.java

@@ -46,7 +46,7 @@ public class User {
      */
     public List<Integer> getFolders() {
         if (folders == null) {
-            folders = new ArrayList<Integer>();
+            folders = new ArrayList<>();
         }
         return this.folders;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/Users.java

@@ -28,7 +28,7 @@ public class Users {
      */
     public List<User> getUsers() {
         if (users == null) {
-            users = new ArrayList<User>();
+            users = new ArrayList<>();
         }
         return this.users;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/VideoInfo.java

@@ -31,7 +31,7 @@ public class VideoInfo {
      */
     public List<Captions> getCaptions() {
         if (captions == null) {
-            captions = new ArrayList<Captions>();
+            captions = new ArrayList<>();
         }
         return this.captions;
     }
@@ -58,7 +58,7 @@ public class VideoInfo {
      */
     public List<AudioTrack> getAudioTracks() {
         if (audioTracks == null) {
-            audioTracks = new ArrayList<AudioTrack>();
+            audioTracks = new ArrayList<>();
         }
         return this.audioTracks;
     }
@@ -85,7 +85,7 @@ public class VideoInfo {
      */
     public List<VideoConversion> getConversions() {
         if (conversions == null) {
-            conversions = new ArrayList<VideoConversion>();
+            conversions = new ArrayList<>();
         }
         return this.conversions;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/models/Videos.java

@@ -28,7 +28,7 @@ public class Videos {
      */
     public List<Child> getVideos() {
         if (videos == null) {
-            videos = new ArrayList<Child>();
+            videos = new ArrayList<>();
         }
         return this.videos;
     }

app/src/main/java/com/cappielloantonio/play/subsonic/utils/StringUtil.java

@@ -9,13 +9,13 @@ public class StringUtil {
         try {
             MessageDigest digest = java.security.MessageDigest.getInstance(MD5);
             digest.update(s.getBytes());
-            byte messageDigest[] = digest.digest();
+            byte[] messageDigest = digest.digest();
 
             StringBuilder hexString = new StringBuilder();
             for (byte aMessageDigest : messageDigest) {
-                String h = Integer.toHexString(0xFF & aMessageDigest);
+                StringBuilder h = new StringBuilder(Integer.toHexString(0xFF & aMessageDigest));
                 while (h.length() < 2) {
-                    h = "0" + h;
+                    h.insert(0, "0");
                 }
                 hexString.append(h);
             }

app/src/main/java/com/cappielloantonio/play/subsonic/utils/converter/ErrorCodeConverter.java

@@ -6,7 +6,7 @@ import com.tickaroo.tikxml.TypeConverter;
 public class ErrorCodeConverter implements TypeConverter<ErrorCode> {
     @Override
     public ErrorCode read(String value) throws Exception {
-        return new ErrorCode(Integer.valueOf(value));
+        return new ErrorCode(Integer.parseInt(value));
     }
 
     @Override