import javax.swing.*;
import java.awt.datatransfer.DataFlavor;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetDropEvent;
import java.io.File;
import java.util.List;

public class SimpleDnD extends JFrame {

    public SimpleDnD() {

        setTitle("Drag & Drop Demo");

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

        setSize(500, 500);

        setVisible(true);

        setDropTarget(new DropTarget() {
            @Override
            public void drop(DropTargetDropEvent evt) {
                try {
                    evt.acceptDrop(DnDConstants.ACTION_COPY);
                    List<File> droppedFiles = (List<File>)
                            evt.getTransferable().getTransferData(DataFlavor.javaFileListFlavor);
                    evt.dropComplete(true);
                } catch(Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(SimpleDnD::new);
    }
}