diff --git a/src/main/java/org/schabi/newpipe/extractor/Info.java b/src/main/java/org/schabi/newpipe/extractor/Info.java
index c704717e6..9fa8e130e 100644
--- a/src/main/java/org/schabi/newpipe/extractor/Info.java
+++ b/src/main/java/org/schabi/newpipe/extractor/Info.java
@@ -16,7 +16,7 @@ public abstract class Info implements Serializable {
     public final String url;
     public final String name;
 
-    public List<Throwable> errors = new ArrayList<>();
+    public final List<Throwable> errors = new ArrayList<>();
 
     public void addError(Throwable throwable) {
         this.errors.add(throwable);
diff --git a/src/main/java/org/schabi/newpipe/extractor/Subtitles.java b/src/main/java/org/schabi/newpipe/extractor/Subtitles.java
index 0542b385e..9427bf528 100644
--- a/src/main/java/org/schabi/newpipe/extractor/Subtitles.java
+++ b/src/main/java/org/schabi/newpipe/extractor/Subtitles.java
@@ -3,9 +3,10 @@ package org.schabi.newpipe.extractor;
 import org.schabi.newpipe.extractor.stream.SubtitlesFormat;
 
 public class Subtitles {
-    private SubtitlesFormat format;
-    private String languageCode, URL;
-    private boolean autoGenerated;
+    private final SubtitlesFormat format;
+    private final String languageCode;
+    private final String URL;
+    private final boolean autoGenerated;
 
     public Subtitles(SubtitlesFormat format, String languageCode, String URL, boolean autoGenerated) {
         this.format = format;
diff --git a/src/main/java/org/schabi/newpipe/extractor/SuggestionExtractor.java b/src/main/java/org/schabi/newpipe/extractor/SuggestionExtractor.java
index 983adc07e..d7c9cdca7 100644
--- a/src/main/java/org/schabi/newpipe/extractor/SuggestionExtractor.java
+++ b/src/main/java/org/schabi/newpipe/extractor/SuggestionExtractor.java
@@ -27,7 +27,7 @@ import java.util.List;
 
 public abstract class SuggestionExtractor {
 
-    private int serviceId;
+    private final int serviceId;
 
     public SuggestionExtractor(int serviceId) {
         this.serviceId = serviceId;
diff --git a/src/main/java/org/schabi/newpipe/extractor/kiosk/KioskExtractor.java b/src/main/java/org/schabi/newpipe/extractor/kiosk/KioskExtractor.java
index 5df579e7a..923f5d033 100644
--- a/src/main/java/org/schabi/newpipe/extractor/kiosk/KioskExtractor.java
+++ b/src/main/java/org/schabi/newpipe/extractor/kiosk/KioskExtractor.java
@@ -30,7 +30,7 @@ import java.io.IOException;
 
 public abstract class KioskExtractor extends ListExtractor {
     private String contentCountry = null;
-    private String id = null;
+    private final String id;
 
     public KioskExtractor(StreamingService streamingService,
                           String url,
diff --git a/src/main/java/org/schabi/newpipe/extractor/kiosk/KioskList.java b/src/main/java/org/schabi/newpipe/extractor/kiosk/KioskList.java
index bbaab0092..5256af8e0 100644
--- a/src/main/java/org/schabi/newpipe/extractor/kiosk/KioskList.java
+++ b/src/main/java/org/schabi/newpipe/extractor/kiosk/KioskList.java
@@ -19,8 +19,8 @@ public  class KioskList {
             throws ExtractionException, IOException;
     }
 
-    private int service_id;
-    private HashMap<String, KioskEntry> kioskList = new HashMap<>();
+    private final int service_id;
+    private final HashMap<String, KioskEntry> kioskList = new HashMap<>();
     private String defaultKiosk = null;
 
     private class KioskEntry {
@@ -28,8 +28,8 @@ public  class KioskList {
             extractorFactory = ef;
             handler = h;
         }
-        KioskExtractorFactory extractorFactory;
-        UrlIdHandler handler;
+        final KioskExtractorFactory extractorFactory;
+        final UrlIdHandler handler;
     }
 
     public KioskList(int service_id) {
diff --git a/src/main/java/org/schabi/newpipe/extractor/search/SearchEngine.java b/src/main/java/org/schabi/newpipe/extractor/search/SearchEngine.java
index b9f9fa393..878888324 100644
--- a/src/main/java/org/schabi/newpipe/extractor/search/SearchEngine.java
+++ b/src/main/java/org/schabi/newpipe/extractor/search/SearchEngine.java
@@ -35,7 +35,7 @@ public abstract class SearchEngine {
         }
     }
 
-    private InfoItemSearchCollector collector;
+    private final InfoItemSearchCollector collector;
 
     public SearchEngine(int serviceId) {
         collector = new InfoItemSearchCollector(serviceId);
diff --git a/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudChannelInfoItemExtractor.java b/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudChannelInfoItemExtractor.java
index 773e8e405..532c059b8 100644
--- a/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudChannelInfoItemExtractor.java
+++ b/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudChannelInfoItemExtractor.java
@@ -4,7 +4,7 @@ import com.grack.nanojson.JsonObject;
 import org.schabi.newpipe.extractor.channel.ChannelInfoItemExtractor;
 
 public class SoundcloudChannelInfoItemExtractor implements ChannelInfoItemExtractor {
-    private JsonObject searchResult;
+    private final JsonObject searchResult;
 
     public SoundcloudChannelInfoItemExtractor(JsonObject searchResult) {
         this.searchResult = searchResult;
diff --git a/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudPlaylistInfoItemExtractor.java b/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudPlaylistInfoItemExtractor.java
index 6002f054e..276f2c6a5 100644
--- a/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudPlaylistInfoItemExtractor.java
+++ b/src/main/java/org/schabi/newpipe/extractor/services/soundcloud/SoundcloudPlaylistInfoItemExtractor.java
@@ -9,7 +9,7 @@ public class SoundcloudPlaylistInfoItemExtractor implements PlaylistInfoItemExtr
     private static final String AVATAR_URL_KEY = "avatar_url";
     private static final String ARTWORK_URL_KEY = "artwork_url";
 
-    private JsonObject searchResult;
+    private final JsonObject searchResult;
 
     public SoundcloudPlaylistInfoItemExtractor(JsonObject searchResult) {
         this.searchResult = searchResult;
diff --git a/src/main/java/org/schabi/newpipe/extractor/services/youtube/ItagItem.java b/src/main/java/org/schabi/newpipe/extractor/services/youtube/ItagItem.java
index 9d9663de3..1950c0b5e 100644
--- a/src/main/java/org/schabi/newpipe/extractor/services/youtube/ItagItem.java
+++ b/src/main/java/org/schabi/newpipe/extractor/services/youtube/ItagItem.java
@@ -146,8 +146,8 @@ public class ItagItem {
         return mediaFormat;
     }
 
-    public int id;
-    public ItagType itagType;
+    public final int id;
+    public final ItagType itagType;
 
     // Audio fields
     public int avgBitrate = -1;
diff --git a/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeChannelInfoItemExtractor.java b/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeChannelInfoItemExtractor.java
index d6d5d4620..a04d85622 100644
--- a/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeChannelInfoItemExtractor.java
+++ b/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeChannelInfoItemExtractor.java
@@ -26,7 +26,7 @@ import org.schabi.newpipe.extractor.utils.Utils;
  */
 
 public class YoutubeChannelInfoItemExtractor implements ChannelInfoItemExtractor {
-    private Element el;
+    private final Element el;
 
     public YoutubeChannelInfoItemExtractor(Element el) {
         this.el = el;
diff --git a/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubePlaylistInfoItemExtractor.java b/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubePlaylistInfoItemExtractor.java
index 552f58f41..fe6e7768f 100644
--- a/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubePlaylistInfoItemExtractor.java
+++ b/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubePlaylistInfoItemExtractor.java
@@ -6,7 +6,7 @@ import org.schabi.newpipe.extractor.playlist.PlaylistInfoItemExtractor;
 import org.schabi.newpipe.extractor.utils.Utils;
 
 public class YoutubePlaylistInfoItemExtractor implements PlaylistInfoItemExtractor {
-    private Element el;
+    private final Element el;
 
     public YoutubePlaylistInfoItemExtractor(Element el) {
         this.el = el;
diff --git a/src/main/java/org/schabi/newpipe/extractor/stream/SubtitlesFormat.java b/src/main/java/org/schabi/newpipe/extractor/stream/SubtitlesFormat.java
index a45454800..1509d339d 100644
--- a/src/main/java/org/schabi/newpipe/extractor/stream/SubtitlesFormat.java
+++ b/src/main/java/org/schabi/newpipe/extractor/stream/SubtitlesFormat.java
@@ -13,8 +13,8 @@ public enum SubtitlesFormat {
     TRANSCRIPT2 (0x3, "srv2"),
     TRANSCRIPT3 (0x4, "srv3");
 
-    private int id;
-    private String extension;
+    private final int id;
+    private final String extension;
 
     SubtitlesFormat(int id, String extension) {
         this.id = id;
diff --git a/src/main/java/org/schabi/newpipe/extractor/stream/VideoStream.java b/src/main/java/org/schabi/newpipe/extractor/stream/VideoStream.java
index 76fa20c1a..1e877bee3 100644
--- a/src/main/java/org/schabi/newpipe/extractor/stream/VideoStream.java
+++ b/src/main/java/org/schabi/newpipe/extractor/stream/VideoStream.java
@@ -23,8 +23,8 @@ package org.schabi.newpipe.extractor.stream;
 import org.schabi.newpipe.extractor.MediaFormat;
 
 public class VideoStream extends Stream {
-    public String resolution;
-    public boolean isVideoOnly;
+    public final String resolution;
+    public final boolean isVideoOnly;
 
 
     public VideoStream(String url, MediaFormat format, String resolution) {