docs: Add warning about internal classes.

core/src/main/java/com/google/cloud/sql/core/CoreSocketFactory.java

@@ -19,8 +19,9 @@
 import com.google.cloud.sql.ConnectionConfig;
 
 /**
- * Implementation of informally used java API to preserve compatibility with older code that uses
- * CoreSocketFactory.
+ * WARNING: This class is not a stable, public Java API. The class definition may change without
+ * notice. Implementation of informally used java API to preserve compatibility with older code that
+ * uses CoreSocketFactory.
  *
  * @deprecated This will soon be replaced.
  */

core/src/main/java/com/google/cloud/sql/core/InternalConnectorRegistry.java

@@ -50,7 +50,7 @@
  * <p>This class should not be used directly, but only through the JDBC driver specific {@code
  * SocketFactory} implementations.
  *
- * <p>The API of this class is subject to change without notice.
+ * <p>WARNING: This is an internal class. The API is subject to change without notice.
  */
 public final class InternalConnectorRegistry {
   static final long DEFAULT_MAX_REFRESH_MS = 30000;

core/src/main/java/com/google/cloud/sql/core/package-info.java

@@ -15,8 +15,10 @@
  */
 
 /**
- * Package com.google.cloud.sql.core holds internal shared packages that implement logic to create a
- * socket to a Cloud SQL database. Classes in this package are considered internal and subject to
+ * WARNING: This package does not contain any stable, public Java API. The class definitions may
  * change without notice.
+ *
+ * <p>Package com.google.cloud.sql.core holds internal shared packages that implement logic to
+ * create a socket to a Cloud SQL database.
  */
 package com.google.cloud.sql.core;