diff --git a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/AndroidMediaPlayer.java b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/AndroidMediaPlayer.java
index 7f59329c502b6909885eb0b059b7387a73ea7e8d..693df7b508300194d5a55bbfa7cf22c9bdeee047 100644
--- a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/AndroidMediaPlayer.java
+++ b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/AndroidMediaPlayer.java
@@ -39,12 +39,12 @@ import tv.danmaku.ijk.media.player.misc.ITrackInfo;
 import tv.danmaku.ijk.media.player.pragma.DebugLog;
 
 public class AndroidMediaPlayer extends AbstractMediaPlayer {
-    private MediaPlayer mInternalMediaPlayer;
-    private AndroidMediaPlayerListenerHolder mInternalListenerAdapter;
+    private final MediaPlayer mInternalMediaPlayer;
+    private final AndroidMediaPlayerListenerHolder mInternalListenerAdapter;
     private String mDataSource;
     private MediaDataSource mMediaDataSource;
 
-    private Object mInitLock = new Object();
+    private final Object mInitLock = new Object();
     private boolean mIsReleased;
 
     private static MediaInfo sMediaInfo;
@@ -121,7 +121,7 @@ public class AndroidMediaPlayer extends AbstractMediaPlayer {
 
     @TargetApi(Build.VERSION_CODES.M)
     private static class MediaDataSourceProxy extends MediaDataSource {
-        private IMediaDataSource mMediaDataSource;
+        private final IMediaDataSource mMediaDataSource;
 
         public MediaDataSourceProxy(IMediaDataSource mediaDataSource) {
             mMediaDataSource = mediaDataSource;
@@ -350,7 +350,7 @@ public class AndroidMediaPlayer extends AbstractMediaPlayer {
             MediaPlayer.OnSeekCompleteListener,
             MediaPlayer.OnVideoSizeChangedListener,
             MediaPlayer.OnErrorListener, MediaPlayer.OnInfoListener {
-        public WeakReference<AndroidMediaPlayer> mWeakMediaPlayer;
+        public final WeakReference<AndroidMediaPlayer> mWeakMediaPlayer;
 
         public AndroidMediaPlayerListenerHolder(AndroidMediaPlayer mp) {
             mWeakMediaPlayer = new WeakReference<AndroidMediaPlayer>(mp);
diff --git a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaCodecInfo.java b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaCodecInfo.java
index 88a45b8168a2018869b31dc0e250b71ba6b69e2d..303ba86a81b57037d56750919cb4aff628d767dc 100644
--- a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaCodecInfo.java
+++ b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaCodecInfo.java
@@ -16,13 +16,13 @@ public class IjkMediaCodecInfo {
     private final static String TAG = "IjkMediaCodecInfo";
 
     public static int RANK_MAX = 1000;
-    public static int RANK_TESTED = 800;
-    public static int RANK_ACCEPTABLE = 700;
-    public static int RANK_LAST_CHANCE = 600;
-    public static int RANK_SECURE = 300;
-    public static int RANK_SOFTWARE = 200;
-    public static int RANK_NON_STANDARD = 100;
-    public static int RANK_NO_SENSE = 0;
+    public static final int RANK_TESTED = 800;
+    public static final int RANK_ACCEPTABLE = 700;
+    public static final int RANK_LAST_CHANCE = 600;
+    public static final int RANK_SECURE = 300;
+    public static final int RANK_SOFTWARE = 200;
+    public static final int RANK_NON_STANDARD = 100;
+    public static final int RANK_NO_SENSE = 0;
 
     public MediaCodecInfo mCodecInfo;
     public int mRank = 0;
diff --git a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaMeta.java b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaMeta.java
index 6527050e626bc29efc1bd08a46dbf15a84d7fe95..07a4e86d6d61b6f3c83e7307ea9201d5990c7ade 100644
--- a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaMeta.java
+++ b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaMeta.java
@@ -115,7 +115,7 @@ public class IjkMediaMeta {
     public long mStartUS;
     public long mBitrate;
 
-    public ArrayList<IjkStreamMeta> mStreams = new ArrayList<IjkStreamMeta>();
+    public final ArrayList<IjkStreamMeta> mStreams = new ArrayList<IjkStreamMeta>();
     public IjkStreamMeta mVideoStream;
     public IjkStreamMeta mAudioStream;
 
@@ -242,7 +242,7 @@ public class IjkMediaMeta {
     public static class IjkStreamMeta {
         public Bundle mMeta;
 
-        public int mIndex;
+        public final int mIndex;
         public String mType;
 
         // common
diff --git a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaPlayer.java b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaPlayer.java
index b3a2987f0a2cd67202e999ac733c5f775882e618..89ecf619f6d758930322be9b018eb35037a7c65d 100644
--- a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaPlayer.java
+++ b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/IjkMediaPlayer.java
@@ -138,7 +138,7 @@ public final class IjkMediaPlayer extends AbstractMediaPlayer {
      * Default library loader
      * Load them by yourself, if your libraries are not installed at default place.
      */
-    private static IjkLibLoader sLocalLibLoader = new IjkLibLoader() {
+    private static final IjkLibLoader sLocalLibLoader = new IjkLibLoader() {
         @Override
         public void loadLibrary(String libName) throws UnsatisfiedLinkError, SecurityException {
             System.loadLibrary(libName);
@@ -810,7 +810,7 @@ public final class IjkMediaPlayer extends AbstractMediaPlayer {
     }
 
     private static class EventHandler extends Handler {
-        private WeakReference<IjkMediaPlayer> mWeakPlayer;
+        private final WeakReference<IjkMediaPlayer> mWeakPlayer;
 
         public EventHandler(IjkMediaPlayer mp, Looper looper) {
             super(looper);
@@ -1047,7 +1047,7 @@ public final class IjkMediaPlayer extends AbstractMediaPlayer {
     }
 
     public static class DefaultMediaCodecSelector implements OnMediaCodecSelectListener {
-        public static DefaultMediaCodecSelector sInstance = new DefaultMediaCodecSelector();
+        public static final DefaultMediaCodecSelector sInstance = new DefaultMediaCodecSelector();
 
         @SuppressWarnings("deprecation")
         @TargetApi(Build.VERSION_CODES.JELLY_BEAN)
diff --git a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/MediaPlayerProxy.java b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/MediaPlayerProxy.java
index d09e30d03e96bc97626641a9693c79382e7128e1..3dfbb1a8b4b2e23181454af051e7f6339e16c6ea 100644
--- a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/MediaPlayerProxy.java
+++ b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/MediaPlayerProxy.java
@@ -31,7 +31,7 @@ import tv.danmaku.ijk.media.player.misc.IMediaDataSource;
 import tv.danmaku.ijk.media.player.misc.ITrackInfo;
 
 public class MediaPlayerProxy implements IMediaPlayer {
-    protected IMediaPlayer mBackEndMediaPlayer;
+    protected final IMediaPlayer mBackEndMediaPlayer;
 
     public MediaPlayerProxy(IMediaPlayer backEndMediaPlayer) {
         mBackEndMediaPlayer = backEndMediaPlayer;
diff --git a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/AndroidMediaFormat.java b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/AndroidMediaFormat.java
index 964600d69f988e7439b177725d1054132afe2bf2..9338a2421beaab64b5d1f6ad8432034684275468 100644
--- a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/AndroidMediaFormat.java
+++ b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/AndroidMediaFormat.java
@@ -21,7 +21,7 @@ import android.media.MediaFormat;
 import android.os.Build;
 
 public class AndroidMediaFormat implements IMediaFormat {
-    private MediaFormat mMediaFormat;
+    private final MediaFormat mMediaFormat;
 
     public AndroidMediaFormat(MediaFormat mediaFormat) {
         mMediaFormat = mediaFormat;
diff --git a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/AndroidTrackInfo.java b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/AndroidTrackInfo.java
index 593eeaa67b887d1561204294065e63f82462e327..bdd88f22a685316e69e461d3a3cc3f3180cf255c 100644
--- a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/AndroidTrackInfo.java
+++ b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/AndroidTrackInfo.java
@@ -22,7 +22,7 @@ import android.media.MediaPlayer;
 import android.os.Build;
 
 public class AndroidTrackInfo implements ITrackInfo {
-    private MediaPlayer.TrackInfo mTrackInfo;
+    private final MediaPlayer.TrackInfo mTrackInfo;
 
     public static AndroidTrackInfo[] fromMediaPlayer(MediaPlayer mp) {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN)
diff --git a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/IjkMediaFormat.java b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/IjkMediaFormat.java
index f0161e8d919984bee5666a8b2a132b42940e7983..401f5aea6035531fd1ccb52dd33a9b5353f32e8b 100644
--- a/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/IjkMediaFormat.java
+++ b/android/ijkplayer/ijkplayer-java/src/main/java/tv/danmaku/ijk/media/player/misc/IjkMediaFormat.java
@@ -44,7 +44,7 @@ public class IjkMediaFormat implements IMediaFormat {
     // Codec
     public static final String CODEC_NAME_H264 = "h264";
 
-    public IjkMediaMeta.IjkStreamMeta mMediaFormat;
+    public final IjkMediaMeta.IjkStreamMeta mMediaFormat;
 
     public IjkMediaFormat(IjkMediaMeta.IjkStreamMeta streamMeta) {
         mMediaFormat = streamMeta;
@@ -91,7 +91,7 @@ public class IjkMediaFormat implements IMediaFormat {
         }
     }
 
-    private static Map<String, Formatter> sFormatterMap = new HashMap<String, Formatter>();
+    private static final Map<String, Formatter> sFormatterMap = new HashMap<String, Formatter>();
 
     {
         sFormatterMap.put(KEY_IJK_CODEC_LONG_NAME_UI, new Formatter() {