Get ArrayList from another Class

what I'm trying to do is: - Scan a directory - For each folder found add its name to an ArrayList - Bring this ArrayList to Main Class and print it.

Here's my ScanDirs Class:

import java.io.File;
import java.util.ArrayList;

public class ScanDirs {

    private ArrayList<String> locations;
    public void scan() {
        File rootDir = new File("./src/data");
        locations = new ArrayList<String>();
        for (File f : rootDir.listFiles()) {
            String fName = f.getName();
            locations.add(fName);
        }
    }
    public ArrayList<String> getScan(){
        return locations;
    }
}

And here's the Main Class:

import java.util.ArrayList;

public class Main {
    private static ScanDirs scanObject;

    public static void main(String[] args) {

        scanObject = new ScanDirs();
        ArrayList<String> list = scanObject.getScan();
        System.out.println(list);

    }

}

My output is: null Why is this happening? Thanks in advance

You haven't called scan() method anywhere in your code. So, simply calling getScan() will result in un-intialized locations value i.e. null.

what you can do is simply call scan() method before calling getScan() method like:

        scanObject = new ScanDirs();
        scanObject.scan();  // calling scan method
        ArrayList<String> list = scanObject.getScan();
        System.out.println(list);