Added Javadoc checks to Checkstyle. Fix violating Javadoc.

build.gradle

@@ -130,7 +130,7 @@ jar {
 }
 
 license {
-    header rootProject.file("HEADER")
+    header rootProject.file("config/license/HEADER")
     ext.year = Calendar.getInstance().get(Calendar.YEAR)
     skipExistingHeaders true
     ignoreFailures true
@@ -235,10 +235,11 @@ jacocoTestReport.dependsOn GCandMem
 build.dependsOn jacocoTestReport
 
 checkstyle {
-    configFile = file("checkstyle.xml")
+    configFile = rootProject.file("config/checkstyle/checkstyle.xml")
     toolVersion = checkstyleVersion
     configProperties = [
-            "checkstyle.header.file": file("HEADER_JAVA")
+            "checkstyle.suppressions.file": rootProject.file("config/checkstyle/suppressions.xml"),
+            "checkstyle.header.file": rootProject.file("config/license/HEADER_JAVA")
     ]
 }
 

checkstyle.xml → config/checkstyle/checkstyle.xml

@@ -4,6 +4,9 @@
         "https://checkstyle.org/dtds/configuration_1_3.dtd">
 
 <module name="Checker">
+    <module name="SuppressionFilter">
+        <property name="file" value="${checkstyle.suppressions.file}"/>
+    </module>
 
     <!-- Headers -->
     <module name="Header">
@@ -12,6 +15,9 @@
     </module>
 
     <module name="TreeWalker">
+        <module name="JavadocMethod"/>
+        <module name="MissingJavadocMethod"/>
+
         <module name="RegexpSinglelineJava">
             <property name="severity" value="warning"/>
             <property name="format" value="^(?!\s+\* $).*?\s+$"/>

config/checkstyle/suppressions.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0"?>
+
+<!DOCTYPE suppressions PUBLIC
+    "-//Checkstyle//DTD SuppressionFilter Configuration 1.2//EN"
+    "https://checkstyle.org/dtds/suppressions_1_2.dtd">
+
+<suppressions>
+
+  <suppress checks="MissingJavadocMethod" files="[\\/]main[\\/]java[\\/]io[\\/]reactivex[\\/]rxjava3[\\/]internal[\\/]"/>
+  <suppress checks="MissingJavadocMethod" files="[\\/]jmh[\\/]java[\\/]io[\\/]reactivex[\\/]rxjava3[\\/]"/>
+  <suppress checks="MissingJavadocMethod" files="[\\/]test[\\/]java[\\/]io[\\/]reactivex[\\/]rxjava3[\\/]"/>
+
+</suppressions>

src/main/java/io/reactivex/rxjava3/core/Completable.java

@@ -1908,11 +1908,12 @@ public final Completable doOnLifecycle(@NonNull Consumer<? super Disposable> onS
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code doOnLifecycle} does not operate by default on a particular {@link Scheduler}.</dd>
      * </dl>
-     * @param onSubscribe the consumer called when a {@link CompletableObserver} subscribes.
-     * @param onError the consumer called when this emits an {@code onError} event
-     * @param onComplete the runnable called just before when the current {@code Completable} completes normally
-     * @param onAfterTerminate the runnable called after this {@code Completable} completes normally
-     * @param onDispose the {@link Runnable} called when the downstream disposes the subscription
+     * @param onSubscribe the {@link Consumer} called when a {@link CompletableObserver} subscribes.
+     * @param onError the {@code Consumer} called when this emits an {@code onError} event
+     * @param onComplete the {@link Action} called just before when the current {@code Completable} completes normally
+     * @param onTerminate the {@code Action} called just before this {@code Completable} terminates
+     * @param onAfterTerminate the {@code Action} called after this {@code Completable} completes normally
+     * @param onDispose the {@code Action} called when the downstream disposes the subscription
      * @return the new {@code Completable} instance
      * @throws NullPointerException if {@code onSubscribe}, {@code onError}, {@code onComplete}
      * {@code onTerminate}, {@code onAfterTerminate} or {@code onDispose} is {@code null}

src/main/java/io/reactivex/rxjava3/core/Flowable.java

@@ -9723,6 +9723,10 @@ public final Flowable<T> doOnComplete(@NonNull Action onComplete) {
      *  <dd>{@code doOnEach} does not operate by default on a particular {@link Scheduler}.</dd>
      * </dl>
      *
+     * @param onNext the {@link Consumer} to invoke when the current {@code Flowable} calls {@code onNext}
+     * @param onError the {@code Consumer} to invoke when the current {@code Flowable} calls {@code onError}
+     * @param onComplete the {@link Action} to invoke when the current {@code Flowable} calls {@code onComplete}
+     * @param onAfterTerminate the {@code Action} to invoke when the current {@code Flowable} calls {@code onAfterTerminate}
      * @return the new {@code Flowable} instance
      * @throws NullPointerException if {@code onNext}, {@code onError}, {@code onComplete} or {@code onAfterTerminate} is {@code null}
      * @see <a href="http://reactivex.io/documentation/operators/do.html">ReactiveX operators documentation: Do</a>

src/main/java/io/reactivex/rxjava3/core/Notification.java

@@ -26,7 +26,9 @@ public final class Notification<T> {
 
     final Object value;
 
-    /** Not meant to be implemented externally. */
+    /** Not meant to be implemented externally.
+     * @param value the value to carry around in the notification, not {@code null}
+     */
     private Notification(@Nullable Object value) {
         this.value = value;
     }

src/main/java/io/reactivex/rxjava3/core/Observable.java

@@ -8608,6 +8608,10 @@ public final Observable<T> doOnComplete(@NonNull Action onComplete) {
      *  <dd>{@code doOnEach} does not operate by default on a particular {@link Scheduler}.</dd>
      * </dl>
      *
+     * @param onNext the {@link Consumer} to invoke when the current {@code Observable} calls {@code onNext}
+     * @param onError the {@code Consumer} to invoke when the current {@code Observable} calls {@code onError}
+     * @param onComplete the {@link Action} to invoke when the current {@code Observable} calls {@code onComplete}
+     * @param onAfterTerminate the {@code Action} to invoke when the current {@code Observable} calls {@code onAfterTerminate}
      * @return the new {@code Observable} instance
      * @throws NullPointerException if {@code onNext}, {@code onError}, {@code onComplete} or {@code onAfterTerminate} is {@code null}
      * @see <a href="http://reactivex.io/documentation/operators/do.html">ReactiveX operators documentation: Do</a>

src/main/java/io/reactivex/rxjava3/exceptions/CompositeException.java

@@ -229,7 +229,9 @@ private void appendStackTrace(StringBuilder b, Throwable ex, String prefix) {
     }
 
     abstract static class PrintStreamOrWriter {
-        /** Prints the specified string as a line on this StreamOrWriter. */
+        /** Prints the specified string as a line on this StreamOrWriter.
+         * @param o string to print
+         */
         abstract void println(Object o);
     }
 

src/main/java/io/reactivex/rxjava3/internal/operators/flowable/FlowableReplay.java

@@ -118,10 +118,11 @@ public static <T> ConnectableFlowable<T> create(Flowable<T> source,
     }
 
     /**
-     * Creates a OperatorReplay instance to replay values of the given source observable.
-     * @param source the source observable
-     * @param bufferFactory the factory to instantiate the appropriate buffer when the observable becomes active
-     * @return the connectable observable
+     * Creates a OperatorReplay instance to replay values of the given source {@code Flowable}.
+     * @param <T> the value type
+     * @param source the source {@code Flowable} to use
+     * @param bufferFactory the factory to instantiate the appropriate buffer when the {@code Flowable} becomes active
+     * @return the {@code ConnectableFlowable} instance
      */
     static <T> ConnectableFlowable<T> create(Flowable<T> source,
             final Supplier<? extends ReplayBuffer<T>> bufferFactory) {
@@ -544,6 +545,7 @@ public void dispose() {
         }
         /**
          * Convenience method to auto-cast the index object.
+         * @param <U> type to cast index object
          * @return the current index object
          */
         @SuppressWarnings("unchecked")

src/main/java/io/reactivex/rxjava3/internal/operators/mixed/ScalarXMapZHelper.java

@@ -78,6 +78,7 @@ static <T> boolean tryAsCompletable(Object source,
      * Try subscribing to a {@link MaybeSource} mapped from
      * a scalar source (which implements {@link Supplier}).
      * @param <T> the upstream value type
+     * @param <R> the downstream value type
      * @param source the source reactive type ({@code Flowable} or {@code Observable})
      *               possibly implementing {@link Supplier}.
      * @param mapper the function that turns the scalar upstream value into a
@@ -117,6 +118,7 @@ static <T, R> boolean tryAsMaybe(Object source,
      * Try subscribing to a {@link SingleSource} mapped from
      * a scalar source (which implements {@link Supplier}).
      * @param <T> the upstream value type
+     * @param <R> the downstream value type
      * @param source the source reactive type ({@code Flowable} or {@code Observable})
      *               possibly implementing {@link Supplier}.
      * @param mapper the function that turns the scalar upstream value into a

src/main/java/io/reactivex/rxjava3/internal/operators/observable/ObservableReplay.java

@@ -122,6 +122,7 @@ public static <T> ConnectableObservable<T> create(ObservableSource<T> source,
 
     /**
      * Creates a OperatorReplay instance to replay values of the given source observable.
+     * @param <T> the value type
      * @param source the source observable
      * @param bufferFactory the factory to instantiate the appropriate buffer when the observable becomes active
      * @return the connectable observable
@@ -453,6 +454,7 @@ public void dispose() {
         }
         /**
          * Convenience method to auto-cast the index object.
+         * @param <U> type index to be casted to
          * @return the index Object or null
          */
         @SuppressWarnings("unchecked")

src/main/java/io/reactivex/rxjava3/internal/util/QueueDrainHelper.java

@@ -291,6 +291,7 @@ static boolean isCancelled(BooleanSupplier cancelled) {
     /**
      * Drains the queue based on the outstanding requests in post-completed mode (only!).
      *
+     * @param <T> the value type
      * @param n the current request amount
      * @param actual the target Subscriber to send events to
      * @param queue the queue to drain if in the post-complete state

src/main/java/io/reactivex/rxjava3/observers/BaseTestConsumer.java

@@ -54,6 +54,9 @@ public abstract class BaseTestConsumer<T, U extends BaseTestConsumer<T, U>> {
      */
     protected boolean timeout;
 
+    /**
+     * Constructs a {@code BaseTestConsumer} with {@code CountDownLatch} set to 1.
+     */
     public BaseTestConsumer() {
         this.values = new VolatileSizeArrayList<>();
         this.errors = new VolatileSizeArrayList<>();

src/test/java/io/reactivex/rxjava3/exceptions/CompositeExceptionTest.java

@@ -148,7 +148,7 @@ public void compositeExceptionFromTwoDuplicateComposites() {
         cex.getCause().printStackTrace();
     }
 
-    /**
+    /*
      * This hijacks the Throwable.printStackTrace() output and puts it in a string, where we can look for
      * "CIRCULAR REFERENCE" (a String added by Throwable.printEnclosedStackTrace)
      */

src/test/java/io/reactivex/rxjava3/schedulers/SchedulerTestHelper.java

@@ -28,6 +28,8 @@ private SchedulerTestHelper() {
     /**
      * Verifies that the given Scheduler does not deliver handled errors to its executing Thread's
      * {@link java.lang.Thread.UncaughtExceptionHandler}.
+     *
+     * @param scheduler {@link Scheduler} to verify.
      */
     static void handledErrorIsNotDeliveredToThreadHandler(Scheduler scheduler) throws InterruptedException {
         Thread.UncaughtExceptionHandler originalHandler = Thread.getDefaultUncaughtExceptionHandler();