--- a/src/java.base/share/classes/sun/net/ftp/impl/FtpClient.java	Thu Dec 13 16:14:07 2018 +0100
+++ b/src/java.base/share/classes/sun/net/ftp/impl/FtpClient.java	Thu Dec 13 15:31:05 2018 +0100
@@ -433,7 +433,7 @@
                 logger.finest("Server [" + serverAddr + "] --> " + response);
             }
 
-            if (response.length() == 0) {
+            if (response.isEmpty()) {
                 code = -1;
             } else {
                 try {
@@ -1049,7 +1049,7 @@
         if (!isConnected()) {
             throw new sun.net.ftp.FtpProtocolException("Not connected yet", FtpReplyCode.BAD_SEQUENCE);
         }
-        if (user == null || user.length() == 0) {
+        if (user == null || user.isEmpty()) {
             throw new IllegalArgumentException("User name can't be null or empty");
         }
         tryLogin(user, password);
@@ -1088,7 +1088,7 @@
         if (!isConnected()) {
             throw new sun.net.ftp.FtpProtocolException("Not connected yet", FtpReplyCode.BAD_SEQUENCE);
         }
-        if (user == null || user.length() == 0) {
+        if (user == null || user.isEmpty()) {
             throw new IllegalArgumentException("User name can't be null or empty");
         }
         tryLogin(user, password);
@@ -1152,7 +1152,7 @@
      * @exception <code>FtpProtocolException</code>
      */
     public sun.net.ftp.FtpClient changeDirectory(String remoteDirectory) throws sun.net.ftp.FtpProtocolException, IOException {
-        if (remoteDirectory == null || "".equals(remoteDirectory)) {
+        if (remoteDirectory == null || remoteDirectory.isEmpty()) {
             throw new IllegalArgumentException("directory can't be null or empty");
         }
 
@@ -1738,7 +1738,7 @@
      * @throws IOException if an error occurs during the transmission.
      */
     public long getSize(String path) throws sun.net.ftp.FtpProtocolException, IOException {
-        if (path == null || path.length() == 0) {
+        if (path == null || path.isEmpty()) {
             throw new IllegalArgumentException("path can't be null or empty");
         }
         issueCommandCheck("SIZE " + path);