import javax.swing.JFrame;
import javax.swing.JOptionPane;
import java.awt.HeadlessException;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetDragEvent;
import java.awt.dnd.DropTargetDropEvent;
import java.awt.dnd.DropTargetEvent;
import java.awt.dnd.DropTargetListener;


public class MainClass extends JFrame implements DropTargetListener
{
    public static void main(String[] args)
    {
        new MainClass();
    }


    public MainClass()
            throws HeadlessException
    {

        new DropTarget(this, DnDConstants.ACTION_COPY_OR_MOVE, this);
        setSize(320, 256);
        setVisible(true);
    }


    @Override
    public void dragEnter(DropTargetDragEvent dtde)
    {
        dtde.acceptDrag(dtde.getDropAction());
    }


    @Override
    public void dragOver(DropTargetDragEvent dtde)
    {
        dtde.acceptDrag(dtde.getDropAction());
    }


    @Override
    public void dropActionChanged(DropTargetDragEvent dtde)
    {
        dtde.acceptDrag(dtde.getDropAction());
    }


    @Override
    public void dragExit(DropTargetEvent dte)
    {
    }


    @Override
    public void drop(DropTargetDropEvent dtde)
    {
        dtde.acceptDrop(dtde.getDropAction());
        JOptionPane.showConfirmDialog(this, "message");
        dtde.dropComplete(true);
    }
}