Use volatile field instead of AtomicReference

it's not necessary to use `AtomicReference` here since the result of atomic method `updateAndGet()` is unused, and not necessary to use `AtomicReferenceFieldUpdater` here since only `set()` is using, volatile field access is more appropriate.

src/main/java/com/zaxxer/hikari/HikariConfig.java

@@ -69,7 +69,7 @@ public class HikariConfig implements HikariConfigMXBean
    private volatile long maxLifetime;
    private volatile int maxPoolSize;
    private volatile int minIdle;
-   private final AtomicReference<Credentials> credentials = new AtomicReference<>(Credentials.of(null, null));
+   private volatile Credentials credentials = Credentials.of(null, null);
 
    // Properties NOT changeable at runtime
    //
@@ -284,7 +284,7 @@ public class HikariConfig implements HikariConfigMXBean
     */
    public String getPassword()
    {
-      return credentials.get().getPassword();
+      return this.credentials.getPassword();
    }
 
    /**
@@ -294,7 +294,8 @@ public class HikariConfig implements HikariConfigMXBean
    @Override
    public void setPassword(String password)
    {
-      credentials.updateAndGet(current -> Credentials.of(current.getUsername(), password));
+      Credentials current = this.credentials;
+      this.credentials = Credentials.of(current.getUsername(), password);
    }
 
    /**
@@ -304,7 +305,7 @@ public class HikariConfig implements HikariConfigMXBean
     */
    public String getUsername()
    {
-      return credentials.get().getUsername();
+      return this.credentials.getUsername();
    }
 
    /**
@@ -315,7 +316,8 @@ public class HikariConfig implements HikariConfigMXBean
    @Override
    public void setUsername(String username)
    {
-      credentials.updateAndGet(current -> Credentials.of(username, current.getPassword()));
+      Credentials current = this.credentials;
+      this.credentials = Credentials.of(username, current.getPassword());
    }
 
    /**
@@ -326,7 +328,7 @@ public class HikariConfig implements HikariConfigMXBean
    @Override
    public void setCredentials(final Credentials credentials)
    {
-      this.credentials.set(credentials);
+      this.credentials = credentials;
    }
 
    /**
@@ -336,7 +338,7 @@ public class HikariConfig implements HikariConfigMXBean
     */
    public Credentials getCredentials()
    {
-      return credentials.get();
+      return this.credentials;
    }
 
    /** {@inheritDoc} */

src/main/java/com/zaxxer/hikari/pool/HikariPool.java

@@ -37,7 +37,6 @@ import java.sql.SQLException;
 import java.sql.SQLTransientConnectionException;
 import java.util.Optional;
 import java.util.concurrent.*;
-import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 
 import static com.zaxxer.hikari.util.ClockSource.*;
 import static com.zaxxer.hikari.util.ConcurrentBag.IConcurrentBagEntry.STATE_IN_USE;
@@ -499,7 +498,7 @@ public final class HikariPool extends PoolBase implements HikariPoolMXBean, IBag
       catch (ConnectionSetupException e) {
          if (poolState == POOL_NORMAL) { // we check POOL_NORMAL to avoid a flood of messages if shutdown() is running concurrently
             logger.error("{} - Error thrown while acquiring connection from data source", poolName, e.getCause());
-            lastConnectionFailure.set(e);
+            lastConnectionFailure = e;
          }
       }
       catch (Exception e) {
@@ -785,8 +784,6 @@ public final class HikariPool extends PoolBase implements HikariPoolMXBean, IBag
    private final class HouseKeeper implements Runnable
    {
       private volatile long previous = plusMillis(currentTime(), -housekeepingPeriodMs);
-      @SuppressWarnings("AtomicFieldUpdaterNotStaticFinal")
-      private final AtomicReferenceFieldUpdater<PoolBase, String> catalogUpdater = AtomicReferenceFieldUpdater.newUpdater(PoolBase.class, String.class, "catalog");
 
       @Override
       public void run()
@@ -798,7 +795,7 @@ public final class HikariPool extends PoolBase implements HikariPoolMXBean, IBag
             leakTaskFactory.updateLeakDetectionThreshold(config.getLeakDetectionThreshold());
 
             if (config.getCatalog() != null && !config.getCatalog().equals(catalog)) {
-               catalogUpdater.set(HikariPool.this, config.getCatalog());
+               HikariPool.this.catalog = config.getCatalog();
             }
 
             final var idleTimeout = config.getIdleTimeout();

src/main/java/com/zaxxer/hikari/pool/PoolBase.java

@@ -41,7 +41,6 @@ import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.ThreadPoolExecutor;
-import java.util.concurrent.atomic.AtomicReference;
 
 import static com.zaxxer.hikari.pool.ProxyConnection.*;
 import static com.zaxxer.hikari.util.ClockSource.*;
@@ -59,7 +58,7 @@ abstract class PoolBase
    protected final String poolName;
 
    volatile String catalog;
-   final AtomicReference<Exception> lastConnectionFailure;
+   volatile Exception lastConnectionFailure;
 
    long connectionTimeout;
    long validationTimeout;
@@ -109,7 +108,6 @@ abstract class PoolBase
       this.poolName = config.getPoolName();
       this.connectionTimeout = config.getConnectionTimeout();
       this.validationTimeout = config.getValidationTimeout();
-      this.lastConnectionFailure = new AtomicReference<>();
 
       initializeDataSource();
    }
@@ -177,7 +175,7 @@ abstract class PoolBase
          return false;
       }
       catch (Exception e) {
-         lastConnectionFailure.set(e);
+         lastConnectionFailure = e;
          logger.warn("{} - Failed to validate connection {} ({}). Possibly consider using a shorter maxLifetime value.",
                      poolName, connection, e.getMessage());
          return true;
@@ -186,7 +184,7 @@ abstract class PoolBase
 
    Exception getLastConnectionFailure()
    {
-      return lastConnectionFailure.get();
+      return lastConnectionFailure;
    }
 
    public DataSource getUnwrappedDataSource()
@@ -365,7 +363,7 @@ abstract class PoolBase
          }
 
          setupConnection(connection);
-         lastConnectionFailure.set(null);
+         lastConnectionFailure = null;
          return connection;
       }
       catch (Exception e) {
@@ -376,7 +374,7 @@ abstract class PoolBase
             logger.debug("{} - Failed to create/setup connection: {}", poolName, e.getMessage());
          }
 
-         lastConnectionFailure.set(e);
+         lastConnectionFailure = e;
          throw e;
       }
       finally {