[Java] Fix return of java doc (#13601)

streaming/java/streaming-api/src/main/java/io/ray/streaming/api/function/Function.java

@@ -11,7 +11,7 @@ public interface Function extends Serializable {
    * storage, and load it back when in fail-over through. {@link
    * Function#loadCheckpoint(Serializable)}.
    *
-   * <p>Returns A serializable object which represents function state.
+   * @return A serializable object which represents function state.
    */
   default Serializable saveCheckpoint() {
     return null;

streaming/java/streaming-api/src/main/java/io/ray/streaming/api/function/impl/FilterFunction.java

@@ -14,8 +14,8 @@ public interface FilterFunction<T> extends Function {
   /**
    * The filter function that evaluates the predicate.
    *
-   * @param value The value to be filtered. Returns True for values that should be retained, false
-   *     for values to be filtered out.
+   * @param value The value to be filtered.
+   * @return True for values that should be retained, false for values to be filtered out.
    */
   boolean filter(T value) throws Exception;
 }

streaming/java/streaming-api/src/main/java/io/ray/streaming/api/partition/Partition.java

@@ -15,8 +15,8 @@ public interface Partition<T> extends Function {
    * record.
    *
    * @param record The record.
-   * @param numPartition num of partitions Returns IDs of the downstream partitions that should
-   *     receive the record.
+   * @param numPartition num of partitions
+   * @return IDs of the downstream partitions that should receive the record.
    */
   int[] partition(T record, int numPartition);
 }

streaming/java/streaming-api/src/main/java/io/ray/streaming/api/stream/DataStream.java

@@ -59,7 +59,8 @@ public class DataStream<T> extends Stream<DataStream<T>, T> {
    * Apply a map function to this stream.
    *
    * @param mapFunction The map function.
-   * @param <R> Type of data returned by the map function. Returns A new DataStream.
+   * @param <R> Type of data returned by the map function.
+   * @return A new DataStream.
    */
   public <R> DataStream<R> map(MapFunction<T, R> mapFunction) {
     return new DataStream<>(this, new MapOperator<>(mapFunction));
@@ -69,7 +70,8 @@ public class DataStream<T> extends Stream<DataStream<T>, T> {
    * Apply a flat-map function to this stream.
    *
    * @param flatMapFunction The FlatMapFunction
-   * @param <R> Type of data returned by the flatmap function. Returns A new DataStream
+   * @param <R> Type of data returned by the flatmap function.
+   * @return A new DataStream
    */
   public <R> DataStream<R> flatMap(FlatMapFunction<T, R> flatMapFunction) {
     return new DataStream<>(this, new FlatMapOperator<>(flatMapFunction));
@@ -84,7 +86,8 @@ public class DataStream<T> extends Stream<DataStream<T>, T> {
    * type with each other.
    *
    * @param stream The DataStream to union output with.
-   * @param others The other DataStreams to union output with. Returns A new UnionStream.
+   * @param others The other DataStreams to union output with.
+   * @return A new UnionStream.
    */
   @SafeVarargs
   public final DataStream<T> union(DataStream<T> stream, DataStream<T>... others) {
@@ -98,7 +101,8 @@ public class DataStream<T> extends Stream<DataStream<T>, T> {
    * Apply union transformations to this stream by merging {@link DataStream} outputs of the same
    * type with each other.
    *
-   * @param streams The DataStreams to union output with. Returns A new UnionStream.
+   * @param streams The DataStreams to union output with.
+   * @return A new UnionStream.
    */
   public final DataStream<T> union(List<DataStream<T>> streams) {
     if (this instanceof UnionStream) {
@@ -115,7 +119,8 @@ public class DataStream<T> extends Stream<DataStream<T>, T> {
    *
    * @param other Another stream.
    * @param <O> The type of the other stream data.
-   * @param <R> The type of the data in the joined stream. Returns A new JoinStream.
+   * @param <R> The type of the data in the joined stream.
+   * @return A new JoinStream.
    */
   public <O, R> JoinStream<T, O, R> join(DataStream<O> other) {
     return new JoinStream<>(this, other);
@@ -129,7 +134,8 @@ public class DataStream<T> extends Stream<DataStream<T>, T> {
   /**
    * Apply a sink function and get a StreamSink.
    *
-   * @param sinkFunction The sink function. Returns A new StreamSink.
+   * @param sinkFunction The sink function.
+   * @return A new StreamSink.
    */
   public DataStreamSink<T> sink(SinkFunction<T> sinkFunction) {
     return new DataStreamSink<>(this, new SinkOperator<>(sinkFunction));
@@ -139,7 +145,8 @@ public class DataStream<T> extends Stream<DataStream<T>, T> {
    * Apply a key-by function to this stream.
    *
    * @param keyFunction the key function.
-   * @param <K> The type of the key. Returns A new KeyDataStream.
+   * @param <K> The type of the key.
+   * @return A new KeyDataStream.
    */
   public <K> KeyDataStream<K, T> keyBy(KeyFunction<T, K> keyFunction) {
     checkPartitionCall();
@@ -149,7 +156,7 @@ public class DataStream<T> extends Stream<DataStream<T>, T> {
   /**
    * Apply broadcast to this stream.
    *
-   * <p>Returns This stream.
+   * @return This stream.
    */
   public DataStream<T> broadcast() {
     checkPartitionCall();
@@ -159,7 +166,8 @@ public class DataStream<T> extends Stream<DataStream<T>, T> {
   /**
    * Apply a partition to this stream.
    *
-   * @param partition The partitioning strategy. Returns This stream.
+   * @param partition The partitioning strategy.
+   * @return This stream.
    */
   public DataStream<T> partitionBy(Partition<T> partition) {
     checkPartitionCall();

streaming/java/streaming-api/src/main/java/io/ray/streaming/api/stream/DataStreamSource.java

@@ -27,7 +27,8 @@ public class DataStreamSource<T> extends DataStream<T> implements StreamSource<T
    *
    * @param context Stream context.
    * @param values A collection of values.
-   * @param <T> The type of source data. Returns A DataStreamSource.
+   * @param <T> The type of source data.
+   * @return A DataStreamSource.
    */
   public static <T> DataStreamSource<T> fromCollection(
       StreamingContext context, Collection<T> values) {

streaming/java/streaming-api/src/main/java/io/ray/streaming/api/stream/KeyDataStream.java

@@ -33,7 +33,8 @@ public class KeyDataStream<K, T> extends DataStream<T> {
   /**
    * Apply a reduce function to this stream.
    *
-   * @param reduceFunction The reduce function. Returns A new DataStream.
+   * @param reduceFunction The reduce function.
+   * @return A new DataStream.
    */
   public DataStream<T> reduce(ReduceFunction reduceFunction) {
     return new DataStream<>(this, new ReduceOperator(reduceFunction));
@@ -44,7 +45,8 @@ public class KeyDataStream<K, T> extends DataStream<T> {
    *
    * @param aggregateFunction The aggregate function
    * @param <A> The type of aggregated intermediate data.
-   * @param <O> The type of result data. Returns A new DataStream.
+   * @param <O> The type of result data.
+   * @return A new DataStream.
    */
   public <A, O> DataStream<O> aggregate(AggregateFunction<T, A, O> aggregateFunction) {
     return new DataStream<>(this, null);

streaming/java/streaming-api/src/main/java/io/ray/streaming/jobgraph/JobGraph.java

@@ -43,7 +43,7 @@ public class JobGraph implements Serializable {
    * Generate direct-graph(made up of a set of vertices and connected by edges) by current job graph
    * for simple log printing.
    *
-   * <p>Returns Digraph in string type.
+   * @return Digraph in string type.
    */
   public String generateDigraph() {
     StringBuilder digraph = new StringBuilder();

streaming/java/streaming-api/src/main/java/io/ray/streaming/python/stream/PythonDataStream.java

@@ -51,7 +51,8 @@ public class PythonDataStream extends Stream<PythonDataStream, Object> implement
   /**
    * Apply a map function to this stream.
    *
-   * @param func The python MapFunction. Returns A new PythonDataStream.
+   * @param func The python MapFunction.
+   * @return A new PythonDataStream.
    */
   public PythonDataStream map(PythonFunction func) {
     func.setFunctionInterface(FunctionInterface.MAP_FUNCTION);
@@ -65,7 +66,8 @@ public class PythonDataStream extends Stream<PythonDataStream, Object> implement
   /**
    * Apply a flat-map function to this stream.
    *
-   * @param func The python FlapMapFunction. Returns A new PythonDataStream
+   * @param func The python FlapMapFunction.
+   * @return A new PythonDataStream
    */
   public PythonDataStream flatMap(PythonFunction func) {
     func.setFunctionInterface(FunctionInterface.FLAT_MAP_FUNCTION);
@@ -79,8 +81,9 @@ public class PythonDataStream extends Stream<PythonDataStream, Object> implement
   /**
    * Apply a filter function to this stream.
    *
-   * @param func The python FilterFunction. Returns A new PythonDataStream that contains only the
-   *     elements satisfying the given filter predicate.
+   * @param func The python FilterFunction.
+   * @return A new PythonDataStream that contains only the elements satisfying the given filter
+   *     predicate.
    */
   public PythonDataStream filter(PythonFunction func) {
     func.setFunctionInterface(FunctionInterface.FILTER_FUNCTION);
@@ -92,7 +95,8 @@ public class PythonDataStream extends Stream<PythonDataStream, Object> implement
    * same type with each other.
    *
    * @param stream The DataStream to union output with.
-   * @param others The other DataStreams to union output with. Returns A new UnionStream.
+   * @param others The other DataStreams to union output with.
+   * @return A new UnionStream.
    */
   public final PythonDataStream union(PythonDataStream stream, PythonDataStream... others) {
     List<PythonDataStream> streams = new ArrayList<>();
@@ -105,7 +109,8 @@ public class PythonDataStream extends Stream<PythonDataStream, Object> implement
    * Apply union transformations to this stream by merging {@link PythonDataStream} outputs of the
    * same type with each other.
    *
-   * @param streams The DataStreams to union output with. Returns A new UnionStream.
+   * @param streams The DataStreams to union output with.
+   * @return A new UnionStream.
    */
   public final PythonDataStream union(List<PythonDataStream> streams) {
     if (this instanceof PythonUnionStream) {
@@ -124,7 +129,8 @@ public class PythonDataStream extends Stream<PythonDataStream, Object> implement
   /**
    * Apply a sink function and get a StreamSink.
    *
-   * @param func The python SinkFunction. Returns A new StreamSink.
+   * @param func The python SinkFunction.
+   * @return A new StreamSink.
    */
   public PythonStreamSink sink(PythonFunction func) {
     func.setFunctionInterface(FunctionInterface.SINK_FUNCTION);
@@ -138,7 +144,8 @@ public class PythonDataStream extends Stream<PythonDataStream, Object> implement
   /**
    * Apply a key-by function to this stream.
    *
-   * @param func the python keyFunction. Returns A new KeyDataStream.
+   * @param func the python keyFunction.
+   * @return A new KeyDataStream.
    */
   public PythonKeyDataStream keyBy(PythonFunction func) {
     checkPartitionCall();
@@ -149,7 +156,7 @@ public class PythonDataStream extends Stream<PythonDataStream, Object> implement
   /**
    * Apply broadcast to this stream.
    *
-   * <p>Returns This stream.
+   * @return This stream.
    */
   public PythonDataStream broadcast() {
     checkPartitionCall();
@@ -159,7 +166,8 @@ public class PythonDataStream extends Stream<PythonDataStream, Object> implement
   /**
    * Apply a partition to this stream.
    *
-   * @param partition The partitioning strategy. Returns This stream.
+   * @param partition The partitioning strategy.
+   * @return This stream.
    */
   public PythonDataStream partitionBy(PythonPartition partition) {
     checkPartitionCall();

streaming/java/streaming-api/src/main/java/io/ray/streaming/python/stream/PythonKeyDataStream.java

@@ -31,7 +31,8 @@ public class PythonKeyDataStream extends PythonDataStream implements PythonStrea
   /**
    * Apply a reduce function to this stream.
    *
-   * @param func The reduce function. Returns A new DataStream.
+   * @param func The reduce function.
+   * @return A new DataStream.
    */
   public PythonDataStream reduce(PythonFunction func) {
     func.setFunctionInterface(FunctionInterface.REDUCE_FUNCTION);