Restrict string creating object every time

Question

I am working on a method where I need complete folder path like /abc/xyz/mln/ for which I am using recurring method call as below sample code:

public String getFolderDetails(String userid, Long folderId) 
            {
        String folderName = "";
        String folderPath = "";

        try {
                folderName = documentFilesName.getString("name");
                parentFolderId= documentFilesName.getLong("parentFolderId");
                if(documentFilesName.has("parentFolderId"));
                {

                    if(parentFolderId.exist)
                    {
                        folderPath = folderPath+"/"+folderName;
                        getFolderDetails(userid, parentFolderId);
                    }

                }

            }
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
        return folderPath;
    }

but every time folderName and folderPath gets assigned to "" due to recurring it doesn't keep/append the folderName and everytime new value gets assigned to folderPath.

Whats the better approach I can use here? same is happening with StringBuffer/Builder it create new object always.

Narendra Pathai · Accepted Answer · 2015-08-04 10:49:57Z

2

public String getFolderDetails(String userid, Long folderId) {
  // This will be the start of recursion so initializing foldername and folderpath with blank 
  getFolderDetails(userid, folderId, new StringBuilder(""), new StringBuilder(""));
}

// recursive method takes two extra parameters for path and name
private String getFolderDetails(String userid, Long folderId, StringBuilder foldername, StringBuilder folderpath) {
    /// Then each time you dont create a new builder just append to it
}

You need to pass the state i.e. StringBuilders to the recursive method so that it can keep appending to it.

folderpath.append(File.separator).append(folderName);

You should not use '/' as hard coded while using path, as it is file system dependent, rather you should use File.separator for that as shown above.

edited Aug 4, 2015 at 10:49

answered Aug 4, 2015 at 10:44

Narendra Pathai

42.1k18 gold badges88 silver badges122 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

npinti · Accepted Answer · 2015-08-04 10:42:26Z

1

You could provide the folderName and folderPath variables as parameters to your method, thus this: public String getFolderDetails(String userid, Long folderId) becomes this: public String getFolderDetails(String userid, Long folderId, String folderName, String folderPath).

For the first method call, you would provide the empty string variables and then, when you do the recursive call just do getFolderDetails(userid, parentFolderId, folderName, folderPath);

Alternatively, you could have an external StringBuilder which gets populates within the method itself, thus this line: folderPath = folderPath+"/"+folderName; would look something like stringBuilder.append("/").append(folderName);.

answered Aug 4, 2015 at 10:42

npinti

52.2k5 gold badges74 silver badges98 bronze badges

2 Comments

nilFi Over a year ago

thanks :), it sound good and simple solution but again after "return folderPath;" cursor comes to "getFolderDetails(userid, parentFolderId);" how we can stop that?

npinti Over a year ago

@nilFi: Please update your question to show what the problem is.

lance-java · Accepted Answer · 2015-08-06 08:36:47Z

1

You can always avoid recursion by using a stack (LinkedList)

LinkedList<File> stack = new LinkedList<>();
stack.add(root);

while (!stack.isEmpty()) {
    File current = stack.removeFirst();

    ...
    if (someCondition) {
        stack.addLast(someChildFile);
    }
}

edited Aug 6, 2015 at 8:36

answered Aug 4, 2015 at 12:19

lance-java

29.4k6 gold badges73 silver badges114 bronze badges

1 Comment

nilFi Over a year ago

it seems interesting but I am bit confused here and unable to understand how it can work.

Collectives™ on Stack Overflow

Restrict string creating object every time

3 Answers 3

Comments

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related