java : Arrange and retrieve data using HashMap and List

Question

I have data like in following logical format:

FolderID-1
    FileID-1
    FileID-2    
FolderID-2
    FileID-3
    FileID-4
    FileID-5
    FileID-6    
FolderID-3
    FileID-7
    FileID-8
    FileID-9
    FileID-10

I have list of FileID object which have FoldeID I need to update one field in this list and need to pass to this list in other method.

I need to get FileID object based on fileid & folderid in that method. To achieve the same I know two way
1 HashMap<folderid,List<FileID>> OR 2 HashMap<folderid, HashMap<fileid ,FileID>

Is there any other efficient way to do the same? Thanks for looking here.

Answer 1

Hi I read your cmnt you can go ahead with the string key (using fileid and folder id) that will work for you. But your data comes with a nice logical structure . file id and folder id will be unique as well as a single folder will contain file having the file id is consecutive. So, My approach to solve this entirely depends on this structure.

I made two Class FileIdObj and FolderIdObj thats contains the data redarding the file and folder respectively.

public static void fileIdBasedOnFileIdAndFolderId( List<FileIdObj> fileList)
    {
        Map<Integer,FolderIdObj> folderIdMap=new HashMap<Integer,FolderIdObj>();
        Map<Integer,FileIdObj> fileIdMap=new HashMap<Integer,FileIdObj>();

        for(int i=0;i<fileList.size();i++)
        {
            FileIdObj file=fileList.get(i);
            fileIdMap.put(file.getFileId(), file);

            int folderId=file.getFolderId();
            FolderIdObj folder=new FolderIdObj();

            if(folderIdMap.containsKey(folderId))
            {
                folder=folderIdMap.get(folderId);
                folder.setEndFileId(file.getFileId());
            }else
            {
                folder.setFolderId(folderId);
                folder.setStartFileId(file.getFileId());
                folder.setEndFileId(file.getFileId());
            }

            folderIdMap.put(folderId, folder);
        }

        Set<Integer> set=folderIdMap.keySet();
        Iterator it=set.iterator();
        while(it.hasNext())
        {
            FolderIdObj obj=folderIdMap.get(it.next());
            System.out.println("folder id: "+obj.getFolderId()+" start fileId: "+obj.getStartFileId()+
                    " end fileId: "+obj.getEndFileId());
        }

        System.out.println();
        System.out.println();

        set=fileIdMap.keySet();
        it=set.iterator();
        while(it.hasNext())
        {
            FileIdObj obj=fileIdMap.get(it.next());
            System.out.println("file id: "+obj.getFileId()+" folder id:"+obj.getFolderId());
        }
    }

the list on the argument contains the file object only. Please see below for the details of the two class.

public class FileIdObj {

    private int folderId;
    private int fileId;

    public int getFolderId() {
        return folderId;
    }
    public void setFolderId(int folderId) {
        this.folderId = folderId;
    }
    public int getFileId() {
        return fileId;
    }
    public void setFileId(int fileId) {
        this.fileId = fileId;
    }

}
public class FolderIdObj {

    private int folderId;
    private int startFileId;
    private int endFileId;

    public int getFolderId() {
        return folderId;
    }
    public void setFolderId(int folderId) {
        this.folderId = folderId;
    }
    public int getStartFileId() {
        return startFileId;
    }
    public void setStartFileId(int startFileId) {
        this.startFileId = startFileId;
    }
    public int getEndFileId() {
        return endFileId;
    }
    public void setEndFileId(int endFileId) {
        this.endFileId = endFileId;
    }

}