Fix: replace duplicated string literal '/myTopic' with constant (#17419)

Author: A0R0P0I7T

example/mqtt/src/main/java/org/apache/iotdb/mqtt/MQTTClient.java

@@ -27,6 +27,7 @@
 public class MQTTClient {
 
   private static final String DATABASE = "myMqttTest";
+  private static final String MY_TOPIC = "/myTopic";
 
   public static void main(String[] args) throws Exception {
     MQTT mqtt = new MQTT();
@@ -74,39 +75,39 @@ private static void jsonPayloadFormatter(BlockingConnection connection) throws E
   private static void linePayloadFormatter(BlockingConnection connection) throws Exception {
     // myTable,tag1=t1,tag2=t2 fieldKey1="1,2,3" 1740109006001
     String payload = "myTable,tag1=t1,tag2=t2 fieldKey1=\"1,2,3\" 1740109006001";
-    connection.publish(DATABASE + "/myTopic", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
+    connection.publish(DATABASE + MY_TOPIC, payload.getBytes(), QoS.AT_LEAST_ONCE, false);
     Thread.sleep(10);
 
     payload = "myTable,tag1=t1,tag2=t2 fieldKey1=\"1,2,3\" 1740109006002";
-    connection.publish(DATABASE + "/myTopic", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
+    connection.publish(DATABASE + MY_TOPIC, payload.getBytes(), QoS.AT_LEAST_ONCE, false);
     Thread.sleep(10);
 
     payload = "myTable,tag1=t1,tag2=t2 fieldKey1=\"1,2,3\" 1740109006003";
-    connection.publish(DATABASE + "/myTopic", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
+    connection.publish(DATABASE + MY_TOPIC, payload.getBytes(), QoS.AT_LEAST_ONCE, false);
     Thread.sleep(10);
     payload =
         "test1,tag1=t1,tag2=t2 attr3=a5,attr4=a4 field1=\"fieldValue1\",field2=1i,field3=1u 1";
-    connection.publish(DATABASE + "/myTopic", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
+    connection.publish(DATABASE + MY_TOPIC, payload.getBytes(), QoS.AT_LEAST_ONCE, false);
     Thread.sleep(10);
 
     payload = "test1,tag1=t1,tag2=t2  field4=2,field5=2i32,field6=2f 2";
-    connection.publish(DATABASE, payload.getBytes(), QoS.AT_LEAST_ONCE, false);
+    connection.publish(DATABASE + MY_TOPIC, payload.getBytes(), QoS.AT_LEAST_ONCE, false);
     Thread.sleep(10);
 
     payload =
         "test1,tag1=t1,tag2=t2  field7=t,field8=T,field9=true 3 \n "
             + "test1,tag1=t1,tag2=t2  field7=f,field8=F,field9=FALSE 4";
-    connection.publish(DATABASE + "/myTopic", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
+    connection.publish(DATABASE + MY_TOPIC, payload.getBytes(), QoS.AT_LEAST_ONCE, false);
     Thread.sleep(10);
 
     payload =
         "test1,tag1=t1,tag2=t2 attr1=a1,attr2=a2 field1=\"fieldValue1\",field2=1i,field3=1u 4 \n "
             + "test1,tag1=t1,tag2=t2 field4=2,field5=2i32,field6=2f 5";
-    connection.publish(DATABASE + "/myTopic", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
+    connection.publish(DATABASE + MY_TOPIC, payload.getBytes(), QoS.AT_LEAST_ONCE, false);
     Thread.sleep(10);
 
     payload = "# It's a remark\n " + "test1,tag1=t1,tag2=t2 field4=2,field5=2i32,field6=2f 6";
-    connection.publish(DATABASE + "/myTopic", payload.getBytes(), QoS.AT_LEAST_ONCE, false);
+    connection.publish(DATABASE + MY_TOPIC, payload.getBytes(), QoS.AT_LEAST_ONCE, false);
     Thread.sleep(10);
   }
 }