Do some code improvements

Use final where possible, annotate some methods and parameters as Nonnull and format new code to be in the 100 characters limit per line.

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeJavaScriptExtractor.java

@@ -12,11 +12,12 @@ import org.schabi.newpipe.extractor.utils.Parser;
 import javax.annotation.Nonnull;
 
 /**
- * YouTube restricts streaming their media in multiple ways by requiring clients to apply a cipher function
+ * YouTube restricts streaming their media in multiple ways by requiring clients to apply a cipher
- * on parameters of requests.
+ * function on parameters of requests.
  * The cipher function is sent alongside as a JavaScript function.
  * <p>
- * This class handling fetching the JavaScript file in order to allow other classes to extract the needed functions.
+ * This class handling fetching the JavaScript file in order to allow other classes to extract the
+ * needed functions.
  */
 public class YoutubeJavaScriptExtractor {
 
@@ -27,14 +28,16 @@ public class YoutubeJavaScriptExtractor {
     }
 
     /**
-     * Extracts the JavaScript file. The result is cached, so subsequent calls use the result of previous calls.
+     * Extracts the JavaScript file. The result is cached, so subsequent calls use the result of
+     * previous calls.
      *
-     * @param videoId Does not influence the result, but a valid video id may help in the chance that YouTube tracks it.
+     * @param videoId Does not influence the result, but a valid video id may help in the chance
-     * @return The whole javascript file as a string.
+     *                that YouTube tracks it.
+     * @return The whole JavaScript file as a string.
      * @throws ParsingException If the extraction failed.
      */
     @Nonnull
-    public static String extractJavaScriptCode(String videoId) throws ParsingException {
+    public static String extractJavaScriptCode(final String videoId) throws ParsingException {
         if (cachedJavaScriptCode == null) {
             final String playerJsUrl = YoutubeJavaScriptExtractor.cleanJavaScriptUrl(
                     YoutubeJavaScriptExtractor.extractJavaScriptUrl(videoId));
@@ -45,18 +48,19 @@ public class YoutubeJavaScriptExtractor {
     }
 
     /**
-     * Same as {@link YoutubeJavaScriptExtractor#extractJavaScriptCode(String)} but with a constant value for videoId.
+     * Same as {@link YoutubeJavaScriptExtractor#extractJavaScriptCode(String)} but with a constant
+     * value for videoId.
      * Possible because the videoId has no influence on the result.
      * <p>
-     * In the off chance that YouTube tracks with which video id the request is made, it may make sense to pass in
+     * In the off chance that YouTube tracks with which video id the request is made, it may make
-     * video ids.
+     * sense to pass in video ids.
      */
     @Nonnull
     public static String extractJavaScriptCode() throws ParsingException {
         return extractJavaScriptCode("d4IGg5dqeO8");
     }
 
-    private static String extractJavaScriptUrl(String videoId) throws ParsingException {
+    private static String extractJavaScriptUrl(final String videoId) throws ParsingException {
         try {
             final String embedUrl = "https://www.youtube.com/embed/" + videoId;
             final String embedPageContent = NewPipe.getDownloader()
@@ -84,7 +88,8 @@ public class YoutubeJavaScriptExtractor {
         throw new ParsingException("Embedded info did not provide YouTube player js url");
     }
 
-    private static String cleanJavaScriptUrl(String playerJsUrl) {
+    @Nonnull
+    private static String cleanJavaScriptUrl(@Nonnull final String playerJsUrl) {
         if (playerJsUrl.startsWith("//")) {
             return HTTPS + playerJsUrl;
         } else if (playerJsUrl.startsWith("/")) {
@@ -95,10 +100,12 @@ public class YoutubeJavaScriptExtractor {
         }
     }
 
-    private static String downloadJavaScriptCode(String playerJsUrl) throws ParsingException {
+    @Nonnull
+    private static String downloadJavaScriptCode(final String playerJsUrl)
+            throws ParsingException {
         try {
             return NewPipe.getDownloader().get(playerJsUrl, Localization.DEFAULT).responseBody();
-        } catch (Exception e) {
+        } catch (final Exception e) {
             throw new ParsingException("Could not get player js code from url: " + playerJsUrl);
         }
     }

extractor/src/main/java/org/schabi/newpipe/extractor/services/youtube/YoutubeThrottlingDecrypter.java

@@ -4,6 +4,7 @@ import org.schabi.newpipe.extractor.exceptions.ParsingException;
 import org.schabi.newpipe.extractor.utils.JavaScript;
 import org.schabi.newpipe.extractor.utils.Parser;
 
+import javax.annotation.Nonnull;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.regex.Pattern;
@@ -33,11 +34,12 @@ public class YoutubeThrottlingDecrypter {
 
     /**
      * <p>
-     * Use this if you care about the off chance that YouTube tracks with which videoId the cipher is requested.
+     * Use this if you care about the off chance that YouTube tracks with which videoId the cipher
+     * is requested.
      * </p>
      * Otherwise use the no-arg constructor which uses a constant value.
      */
-    public YoutubeThrottlingDecrypter(String videoId) throws ParsingException {
+    public YoutubeThrottlingDecrypter(final String videoId) throws ParsingException {
         final String playerJsCode = YoutubeJavaScriptExtractor.extractJavaScriptCode(videoId);
 
         functionName = parseDecodeFunctionName(playerJsCode);
@@ -51,17 +53,22 @@ public class YoutubeThrottlingDecrypter {
         function = parseDecodeFunction(playerJsCode, functionName);
     }
 
-    private String parseDecodeFunctionName(String playerJsCode) throws Parser.RegexException {
+    private String parseDecodeFunctionName(final String playerJsCode)
-        Pattern pattern = Pattern.compile("b=a\\.get\\(\"n\"\\)\\)&&\\(b=(\\w+)\\(b\\),a\\.set\\(\"n\",b\\)");
+            throws Parser.RegexException {
+        Pattern pattern = Pattern.compile(
+                "b=a\\.get\\(\"n\"\\)\\)&&\\(b=(\\w+)\\(b\\),a\\.set\\(\"n\",b\\)");
         return Parser.matchGroup1(pattern, playerJsCode);
     }
 
-    private String parseDecodeFunction(String playerJsCode, String functionName) throws Parser.RegexException {
+    @Nonnull
-        Pattern functionPattern = Pattern.compile(functionName + "=function(.*?;)\n", Pattern.DOTALL);
+    private String parseDecodeFunction(final String playerJsCode, final String functionName)
-        return  "function " + functionName + Parser.matchGroup1(functionPattern, playerJsCode);
+            throws Parser.RegexException {
+        Pattern functionPattern = Pattern.compile(functionName + "=function(.*?;)\n",
+                Pattern.DOTALL);
+        return "function " + functionName + Parser.matchGroup1(functionPattern, playerJsCode);
     }
 
-    public String apply(String url) throws Parser.RegexException {
+    public String apply(final String url) throws Parser.RegexException {
         if (containsNParam(url)) {
             String oldNParam = parseNParam(url);
             String newNParam = decryptNParam(oldNParam);
@@ -71,16 +78,16 @@ public class YoutubeThrottlingDecrypter {
         }
     }
 
-    private boolean containsNParam(String url) {
+    private boolean containsNParam(final String url) {
         return Parser.isMatch(N_PARAM_REGEX, url);
     }
 
-    private String parseNParam(String url) throws Parser.RegexException {
+    private String parseNParam(final String url) throws Parser.RegexException {
         Pattern nValuePattern = Pattern.compile(N_PARAM_REGEX);
         return Parser.matchGroup1(nValuePattern, url);
     }
 
-    private String decryptNParam(String nParam) {
+    private String decryptNParam(final String nParam) {
         if (nParams.containsKey(nParam)) {
             return nParams.get(nParam);
         }
@@ -89,7 +96,10 @@ public class YoutubeThrottlingDecrypter {
         return decryptedNParam;
     }
 
-    private String replaceNParam(String url, String oldValue, String newValue) {
+    @Nonnull
+    private String replaceNParam(@Nonnull final String url,
+                                 final String oldValue,
+                                 final String newValue) {
         return url.replace(oldValue, newValue);
     }
 }

extractor/src/main/java/org/schabi/newpipe/extractor/utils/JavaScript.java

@@ -9,15 +9,17 @@ public class JavaScript {
     private JavaScript() {
     }
 
-    public static String run(String function, String functionName, String... parameters) {
+    public static String run(final String function,
+                             final String functionName,
+                             final String... parameters) {
         try {
-            Context context = Context.enter();
+            final Context context = Context.enter();
             context.setOptimizationLevel(-1);
-            ScriptableObject scope = context.initSafeStandardObjects();
+            final ScriptableObject scope = context.initSafeStandardObjects();
 
             context.evaluateString(scope, function, functionName, 1, null);
-            Function jsFunction = (Function) scope.get(functionName, scope);
+            final Function jsFunction = (Function) scope.get(functionName, scope);
-            Object result = jsFunction.call(context, scope, scope, parameters);
+            final Object result = jsFunction.call(context, scope, scope, parameters);
             return result.toString();
         } finally {
             Context.exit();

extractor/src/test/java/org/schabi/newpipe/extractor/services/youtube/YoutubeJavaScriptExtractorTest.java

@@ -38,7 +38,7 @@ public class YoutubeJavaScriptExtractorTest {
 
     }
 
-    private void assertPlayerJsCode(String playerJsCode) {
+    private void assertPlayerJsCode(final String playerJsCode) {
         assertThat(playerJsCode, allOf(
                 containsString(" Copyright The Closure Library Authors.\n"
                         + " SPDX-License-Identifier: Apache-2.0"),