MINOR: cleanup some warning in Kafka Streams examples (#14547)

Reviewers: Guozhang Wang <wangguoz@gmail.com>

streams/examples/src/main/java/org/apache/kafka/streams/examples/pageview/PageViewTypedDemo.java

@@ -47,32 +47,31 @@ import java.util.concurrent.CountDownLatch;
  * using specific data types (here: JSON POJO; but can also be Avro specific bindings, etc.) for serdes
  * in Kafka Streams.
  *
- * In this example, we join a stream of pageviews (aka clickstreams) that reads from a topic named "streams-pageview-input"
+ * <p>In this example, we join a stream of pageviews (aka clickstreams) that reads from a topic named "streams-pageview-input"
  * with a user profile table that reads from a topic named "streams-userprofile-input", where the data format
  * is JSON string representing a record in the stream or table, to compute the number of pageviews per user region.
  *
- * Before running this example you must create the input topics and the output topic (e.g. via
+ * <p>Before running this example you must create the input topics and the output topic (e.g. via
  * bin/kafka-topics --create ...), and write some data to the input topics (e.g. via
  * bin/kafka-console-producer). Otherwise you won't see any data arriving in the output topic.
  *
- * The inputs for this example are:
+ * <p>The inputs for this example are:
  * - Topic: streams-pageview-input
  *   Key Format: (String) USER_ID
  *   Value Format: (JSON) {"_t": "pv", "user": (String USER_ID), "page": (String PAGE_ID), "timestamp": (long ms TIMESTAMP)}
- *
+ * <p>
  * - Topic: streams-userprofile-input
  *   Key Format: (String) USER_ID
  *   Value Format: (JSON) {"_t": "up", "region": (String REGION), "timestamp": (long ms TIMESTAMP)}
  *
- * To observe the results, read the output topic (e.g., via bin/kafka-console-consumer)
+ * <p>To observe the results, read the output topic (e.g., via bin/kafka-console-consumer)
  * - Topic: streams-pageviewstats-typed-output
  *   Key Format: (JSON) {"_t": "wpvbr", "windowStart": (long ms WINDOW_TIMESTAMP), "region": (String REGION)}
  *   Value Format: (JSON) {"_t": "rc", "count": (long REGION_COUNT), "region": (String REGION)}
  *
- * Note, the "_t" field is necessary to help Jackson identify the correct class for deserialization in the
+ * <p>Note, the "_t" field is necessary to help Jackson identify the correct class for deserialization in the
  * generic {@link JSONSerde}. If you instead specify a specific serde per class, you won't need the extra "_t" field.
  */
-@SuppressWarnings({"WeakerAccess", "unused"})
 public class PageViewTypedDemo {
 
     /**

streams/examples/src/main/java/org/apache/kafka/streams/examples/pageview/PageViewUntypedDemo.java

@@ -45,11 +45,11 @@ import java.util.Properties;
  * using general data types (here: JSON; but can also be Avro generic bindings, etc.) for serdes
  * in Kafka Streams.
  *
- * In this example, we join a stream of pageviews (aka clickstreams) that reads from  a topic named "streams-pageview-input"
+ * <p>In this example, we join a stream of pageviews (aka clickstreams) that reads from  a topic named "streams-pageview-input"
  * with a user profile table that reads from a topic named "streams-userprofile-input", where the data format
  * is JSON string representing a record in the stream or table, to compute the number of pageviews per user region.
  *
- * Before running this example you must create the input topics and the output topic (e.g. via
+ * <p>Before running this example you must create the input topics and the output topic (e.g. via
  * bin/kafka-topics.sh --create ...), and write some data to the input topics (e.g. via
  * bin/kafka-console-producer.sh). Otherwise you won't see any data arriving in the output topic.
  */

streams/examples/src/main/java/org/apache/kafka/streams/examples/pipe/PipeDemo.java

@@ -29,10 +29,10 @@ import java.util.concurrent.CountDownLatch;
  * Demonstrates, using the high-level KStream DSL, how to read data from a source (input) topic and how to
  * write data to a sink (output) topic.
  *
- * In this example, we implement a simple "pipe" program that reads from a source topic "streams-plaintext-input"
+ * <p>In this example, we implement a simple "pipe" program that reads from a source topic "streams-plaintext-input"
  * and writes the data as-is (i.e. unmodified) into a sink topic "streams-pipe-output".
  *
- * Before running this example you must create the input topic and the output topic (e.g. via
+ * <p>Before running this example you must create the input topic and the output topic (e.g. via
  * bin/kafka-topics.sh --create ...), and write some data to the input topic (e.g. via
  * bin/kafka-console-producer.sh). Otherwise you won't see any data arriving in the output topic.
  */
@@ -42,8 +42,8 @@ public class PipeDemo {
         final Properties props = new Properties();
         props.put(StreamsConfig.APPLICATION_ID_CONFIG, "streams-pipe");
         props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
-        props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
-        props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());
+        props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
+        props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
 
         // setting offset reset to earliest so that we can re-run the demo code with the same pre-loaded data
         props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");

streams/examples/src/main/java/org/apache/kafka/streams/examples/temperature/TemperatureDemo.java

@@ -37,26 +37,26 @@ import java.util.concurrent.CountDownLatch;
  * which ingests temperature value to compute the maximum value in the latest TEMPERATURE_WINDOW_SIZE seconds (which
  * is 5 seconds) and send a new message if it exceeds the TEMPERATURE_THRESHOLD (which is 20)
  *
- * In this example, the input stream reads from a topic named "iot-temperature", where the values of messages
+ * <p>In this example, the input stream reads from a topic named "iot-temperature", where the values of messages
  * represent temperature values; using a TEMPERATURE_WINDOW_SIZE seconds "tumbling" window, the maximum value is processed and
  * sent to a topic named "iot-temperature-max" if it exceeds the TEMPERATURE_THRESHOLD.
  *
- * Before running this example you must create the input topic for temperature values in the following way :
+ * <p>Before running this example you must create the input topic for temperature values in the following way :
  *
- * bin/kafka-topics.sh --create --bootstrap-server localhost:9092 --replication-factor 1 --partitions 1 --topic iot-temperature
+ * <p>bin/kafka-topics.sh --create --bootstrap-server localhost:9092 --replication-factor 1 --partitions 1 --topic iot-temperature
  *
- * and at same time create the output topic for filtered values :
+ * <p>and at same time create the output topic for filtered values :
  *
- * bin/kafka-topics.sh --create --bootstrap-server localhost:9092 --replication-factor 1 --partitions 1 --topic iot-temperature-max
+ * <p>bin/kafka-topics.sh --create --bootstrap-server localhost:9092 --replication-factor 1 --partitions 1 --topic iot-temperature-max
  *
- * After that, a console consumer can be started in order to read filtered values from the "iot-temperature-max" topic :
+ * <p>After that, a console consumer can be started in order to read filtered values from the "iot-temperature-max" topic :
  *
  * bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 --topic iot-temperature-max --from-beginning
  *
- * On the other side, a console producer can be used for sending temperature values (which needs to be integers)
+ * <p>On the other side, a console producer can be used for sending temperature values (which needs to be integers)
  * to "iot-temperature" by typing them on the console :
  *
- * bin/kafka-console-producer.sh --bootstrap-server localhost:9092 --topic iot-temperature
+ * <p>bin/kafka-console-producer.sh --bootstrap-server localhost:9092 --topic iot-temperature
  * > 10
  * > 15
  * > 22
@@ -73,8 +73,8 @@ public class TemperatureDemo {
         final Properties props = new Properties();
         props.put(StreamsConfig.APPLICATION_ID_CONFIG, "streams-temperature");
         props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
-        props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
-        props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());
+        props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
+        props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
 
         props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
         props.put(StreamsConfig.STATESTORE_CACHE_MAX_BYTES_CONFIG, 0);

streams/examples/src/main/java/org/apache/kafka/streams/examples/wordcount/WordCountDemo.java

@@ -62,8 +62,8 @@ public final class WordCountDemo {
         props.putIfAbsent(StreamsConfig.APPLICATION_ID_CONFIG, "streams-wordcount");
         props.putIfAbsent(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
         props.putIfAbsent(StreamsConfig.STATESTORE_CACHE_MAX_BYTES_CONFIG, 0);
-        props.putIfAbsent(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
-        props.putIfAbsent(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
+        props.putIfAbsent(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
+        props.putIfAbsent(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
 
         // setting offset reset to earliest so that we can re-run the demo code with the same pre-loaded data
         // Note: To re-run the demo, you need to use the offset reset tool:

streams/examples/src/main/java/org/apache/kafka/streams/examples/wordcount/WordCountProcessorDemo.java

@@ -109,8 +109,8 @@ public final class WordCountProcessorDemo {
         props.putIfAbsent(StreamsConfig.APPLICATION_ID_CONFIG, "streams-wordcount-processor");
         props.putIfAbsent(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
         props.putIfAbsent(StreamsConfig.STATESTORE_CACHE_MAX_BYTES_CONFIG, 0);
-        props.putIfAbsent(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
-        props.putIfAbsent(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());
+        props.putIfAbsent(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
+        props.putIfAbsent(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
 
         // setting offset reset to earliest so that we can re-run the demo code with the same pre-loaded data
         props.putIfAbsent(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");

streams/examples/src/main/java/org/apache/kafka/streams/examples/wordcount/WordCountTransformerDemo.java

@@ -100,9 +100,6 @@ public final class WordCountTransformerDemo {
                         }
                     }
                 }
-
-                @Override
-                public void close() {}
             };
         }
 
@@ -128,8 +125,8 @@ public final class WordCountTransformerDemo {
         props.putIfAbsent(StreamsConfig.APPLICATION_ID_CONFIG, "streams-wordcount-transformer");
         props.putIfAbsent(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
         props.putIfAbsent(StreamsConfig.STATESTORE_CACHE_MAX_BYTES_CONFIG, 0);
-        props.putIfAbsent(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
-        props.putIfAbsent(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());
+        props.putIfAbsent(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
+        props.putIfAbsent(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.StringSerde.class);
 
         // setting offset reset to earliest so that we can re-run the demo code with the same pre-loaded data
         props.putIfAbsent(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");

streams/examples/src/test/java/org/apache/kafka/streams/examples/docs/DeveloperGuideTesting.java

@@ -54,8 +54,8 @@ public class DeveloperGuideTesting {
     private TestOutputTopic<String, Long> outputTopic;
     private KeyValueStore<String, Long> store;
 
-    private Serde<String> stringSerde = new Serdes.StringSerde();
-    private Serde<Long> longSerde = new Serdes.LongSerde();
+    private final Serde<String> stringSerde = new Serdes.StringSerde();
+    private final Serde<Long> longSerde = new Serdes.LongSerde();
 
     @BeforeEach
     public void setup() {
@@ -72,8 +72,8 @@ public class DeveloperGuideTesting {
 
         // setup test driver
         final Properties props = new Properties();
-        props.setProperty(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
-        props.setProperty(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.Long().getClass().getName());
+        props.setProperty(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.StringSerde.class.getName());
+        props.setProperty(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.LongSerde.class.getName());
         testDriver = new TopologyTestDriver(topology, props);
 
         // setup test topics
@@ -155,7 +155,6 @@ public class DeveloperGuideTesting {
         ProcessorContext<String, Long> context;
         private KeyValueStore<String, Long> store;
 
-        @SuppressWarnings("unchecked")
         @Override
         public void init(final ProcessorContext<String, Long> context) {
             this.context = context;