style(gax-grpc): use constant for warning message and simplify comments

Author: lqiu96

sdk-platform-java/gax-java/gax-grpc/src/main/java/com/google/api/gax/grpc/ChannelPool.java

@@ -69,6 +69,11 @@
  * <p>Package-private for internal use.
  */
 class ChannelPool extends ManagedChannel {
+  private static final String CHANNEL_POOL_CONSECUTIVE_RESIZING_WARNING =
+      "Channel pool is repeatedly resizing. "
+          + "Consider adjusting `initialChannelCount` or `maxResizeDelta` to a more reasonable value. "
+          + "See https://docs.cloud.google.com/java/docs/troubleshooting to enable logging "
+          + "and set `com.google.api.gax.grpc.ChannelPool.level=FINEST` to log the channel pool resize behavior.";
   @VisibleForTesting static final Logger LOG = Logger.getLogger(ChannelPool.class.getName());
   private static final java.time.Duration REFRESH_PERIOD = java.time.Duration.ofMinutes(50);
 
@@ -85,16 +90,13 @@ class ChannelPool extends ManagedChannel {
   private final String authority;
 
   // The number of consecutive resize cycles to wait before logging a warning about repeated
-  // resizing.
-  // This is an arbitrary value chosen to detect repeated requests for changes (multiple continuous
-  // increase or decrease attempts) without being too sensitive.
+  // resizing. This is an arbitrary value chosen to detect repeated requests for changes
+  // (multiple continuous increase or decrease attempts) without being too sensitive.
   private static final int CONSECUTIVE_RESIZE_THRESHOLD = 5;
 
   // Tracks the number of consecutive resize cycles where a resize actually occurred (either expand
-  // or shrink).
-  // Used to detect repeated resizing activity and log a warning.
-  // Note: This field is only accessed within the synchronized resize() method, so it does not need
-  // to be atomic.
+  // or shrink). Used to detect repeated resizing activity and log a warning.
+  // Note: This field is only accessed safely within resizeSafely() and does not need to be atomic.
   private int consecutiveResizes = 0;
 
   static ChannelPool create(
@@ -343,14 +345,7 @@ void resize() {
     // Log warning only once when the threshold is reached to avoid spamming logs.
     // Using == instead of >= ensures we don't log on every subsequent resize cycle.
     if (consecutiveResizes == CONSECUTIVE_RESIZE_THRESHOLD) {
-      StringBuilder sb = new StringBuilder();
-      sb.append("Channel pool is repeatedly resizing. ");
-      sb.append(
-          "Consider adjusting `initialChannelCount` or `maxResizeDelta` to a more reasonable value. ");
-      sb.append("See https://docs.cloud.google.com/java/docs/troubleshooting to enable logging ");
-      sb.append(
-          "and set `com.google.api.gax.grpc.ChannelPool.level=FINEST` to log the channel pool resize behavior.");
-      LOG.warning(sb.toString());
+      LOG.warning(CHANNEL_POOL_CONSECUTIVE_RESIZING_WARNING);
     }
 
     // Only resize the pool when thresholds are crossed