Eliminate some String.format() calls. Left one I like for readability.

src/main/java/com/zaxxer/hikari/proxy/ClosedConnection.java

@@ -45,7 +45,7 @@ final class ClosedConnection
                return Boolean.FALSE;
             }
             else if ("toString".equals(methodName)) {
-               return this.getClass().getCanonicalName();
+               return ClosedConnection.class.getCanonicalName();
             }
 
             throw new SQLException("Connection is closed");