Converting File[] to ArrayList

noel

Hi, I've tested in several ways this conversion and the most logical way, seems to me would be by iterating, but it gives the error:

The method add(String) in the type ArrayList is not applicable for the arguments (File)

How to do this, thanks.

ArrayList<String> alfiles = new ArrayList<String>();
File[] files = f.listFiles();
for (File each : files) alfiles.add(each);

koogs

a File is not a String, that's what the error is saying

which do you want?

GoToLoop

Use File::list() in place of File::listFiles(): L-)
https://Docs.Oracle.com/javase/9/docs/api/java/io/File.html#list--

Or better yet, go w/ PApplet::listPaths() instead: \m/
https://Forum.Processing.org/two/discussions/tagged?Tag=listpaths()

noel

Hi, @koogs I have an array obtained by:

String path = "/storage/emulated/legacy/Download"; 
File f = new File(path); 
File[] files = f.listFiles();
printArray(files);

Now I want to convert it to an ArrayList to be used by the KetaiList Class

noel

Hi, @GoToLoop. Using just list() gives me one more error namely

Type mismatch: cannot convert from String[] to File[]

I've read the document of your link and it is a string array, but of a different type (split by commas I think). I'm using it in android so for your second answer I don't think it's applicable.

koogs

so you do want Strings. so use the list() method gotoloop mentioned. only you can't store that in a File[]:

String path = "/storage/emulated/legacy/Download"; 
File f = new File(path); 
String[] files = f.list();
printArray(files);

koogs

it is a string array, but of a different type (split by commas I think)

that's just the output from printArray()

noel

koogs=== The outputs can be like

[1] path/file1 [2]path/file2 etc.

Or [path/file1 , path/file2]

noel

When I use

alfiles.add("path/file1");
alfiles.add("path/file1");
printArray(alfiles);

I get an output like

[ path/file1, path/file2]

And this is accepted by the KetaiList Class

When I convert the File array with

List< File >alfiles = Arrays.asList(files);

I get a simular output [ path/file, etc], but this array is not accepted by the KetaiList Class

PS I had to put a space between < File > , Otherwise it would just disappear in this comment section.

koogs

but this array is not exepted by the KetaiList Class

no, because it's a List of Files, not a List of Strings like it's expecting:

public KetaiList(PApplet _parent, ArrayList<String> data)
public KetaiList(PApplet _parent, String[] data)

don't use a File array, or a File list.

a File is not a String.

GoToLoop

I don't have Android here. ^#(^

But according to @koogs, 1 of the overloaded constructors of class KetaiList can accept a String[] array directly. B-): public KetaiList(PApplet _parent, String[] data)

If that's so, here's my completely untested blind attempt: =P~

final String[] files = listPaths("/storage/emulated/legacy/Download");
printArray(files);
final KetaiList klist = new KetaiList(this, files);

noel

Yes, that's right, it accepts a String[] array directly also. Now it's working. I still would like to know how to convert a File[] array into an ArrayList. List< File >alfiles = Arrays.asList(files); does not work, but I guess this will be for another time. Thank you.

GoToLoop

import java.util.List;
import java.util.Arrays;

final File[] files = new File("/storage/emulated/legacy/Download/").listFiles();
final List<File> lfiles = Arrays.asList(files);

println(lfiles);
exit();

koogs

does not work

not helpful. what is the error?

runnable example, in java, not for android

import java.util.Arrays;
import java.util.List;

File[] fileArray = new File[2];
fileArray[0] = new File("/tmp/a");
fileArray[1] = new File("/tmp/b");

// File[] to List<File>
List<File> fileList1 = Arrays.asList(fileArray);
println("1", fileList1);

// File[] to ArrayList<File>
ArrayList<File> fileList2 = new ArrayList<File>(Arrays.asList(fileArray));
println("2", fileList2);

Arrays.asList returns a List, not an ArrayList so you have to define the class as a List, as per fileList1. and import List

or use the Arrays.asList() to convert to a List, which you can then use in the ArrayList, constructor, as per fileList2

GoToLoop

Another thing to be aware of is that Arrays::asList() returns a fixed-size List: L-)
https://Docs.Oracle.com/javase/9/docs/api/java/util/Arrays.html#asList-T...-

final List<File> lfiles = Arrays.asList(files);

If dynamic-size is needed, pass it as an argument for the ArrayList's constructor: *-:)

final List<File> lfiles = new ArrayList<File>( Arrays.asList(files) );

GoToLoop

public KetaiList(PApplet _parent, ArrayList<String> data)

I wonder why the 2nd parameter is an ArrayList rather than just List. :-O

Any professional library worth its bacon would only request a List, never an ArrayList! :-@

noel

@koogs== Your runnable example will print into the console, but like before will not be accepted by KetaiList (it just won't show up) and doesn't give any error.

noel

@GoToLoop== The last snippet you gave just after my last post will compile, but then crashes with the error:

java.lang.NullPointerException: storage == null

koogs

Well, we only have the code you've posted and we've answered that specific question, "Converting File[] to ArrayList". If you then go on to use the array / ArrayList you haven't shown us that, just vaguely mentioned some android library method you're using.

Post more code for a better chance of a working solution. (But not from me - no android setup)

noel

I have it working now.

import ketai.ui.*;
import android.os.Environment;

KetaiList klist;
String[] files;

void setup() { 
  fullScreen(); 
  textAlign(CENTER); 
  textSize(24);
  text("Click screen to open list.", width/2, height/2);
  String directory = "/Download";
  String path = Environment.getExternalStorageDirectory().toString() + directory;
  files = listPaths(path);
  noLoop();
} 

void draw() {
} 

void mousePressed() { 
  klist = new KetaiList(this, files);
} 

void onKetaiListSelection(KetaiList klist) { 
  String selection = klist.getSelection(); 
  println("Your chosen file is:  " + selection);
}

GoToLoop

https://GitHub.com/ketai/ketai/pull/61