src/java.base/windows/classes/sun/nio/fs/WindowsPath.java

*** 241,257 ****
          // Drive relative path ("C:foo" for example).
          if (isSameDrive(root, getFileSystem().defaultRoot())) {
              // relative to default directory
              String remaining = path.substring(root.length());
              String defaultDirectory = getFileSystem().defaultDirectory();
!             String result;
!             if (defaultDirectory.endsWith("\\")) {
!                 result = defaultDirectory + remaining;
              } else {
!                 result = defaultDirectory + "\\" + remaining;
              }
-             return result;
          } else {
              // relative to some other drive
              String wd;
              try {
                  int dt = GetDriveType(root + "\\");
--- 241,257 ----
          // Drive relative path ("C:foo" for example).
          if (isSameDrive(root, getFileSystem().defaultRoot())) {
              // relative to default directory
              String remaining = path.substring(root.length());
              String defaultDirectory = getFileSystem().defaultDirectory();
!             if (remaining.length() == 0) {
!                 return defaultDirectory;
!             } else if (defaultDirectory.endsWith("\\")) {
!                  return defaultDirectory + remaining;
              } else {
!                 return defaultDirectory + "\\" + remaining;
              }
          } else {
              // relative to some other drive
              String wd;
              try {
                  int dt = GetDriveType(root + "\\");
*** 410,423 ****
--- 410,425 ----
          for (int j=i; j<bn; j++) {
              result.append("..\\");
          }
  
          // append remaining names in child
+         if (!other.isEmpty()) {
              for (int j=i; j<cn; j++) {
                  result.append(other.getName(j).toString());
                  result.append("\\");
              }
+         }
  
          // drop trailing slash in result
          result.setLength(result.length()-1);
          return createFromNormalizedPath(getFileSystem(), result.toString());
      }