import java.awt.datatransfer.*;
import java.awt.dnd.*;

// onDrop: voidfunc(File), but may also return false
static <A extends JComponent> A jHandleFileDrop(A c, final O onDrop) {
  new DropTarget(c, new DropTargetAdapter {
    public void drop(DropTargetDropEvent e) {
      pcall {
        Transferable tr = e.getTransferable();
        DataFlavor[] flavors = tr.getTransferDataFlavors();
        for (DataFlavor flavor : flavors) {
          if (flavor.isFlavorJavaFileListType()) {
            e.acceptDrop(e.getDropAction());
            File file = first((L<File>) tr.getTransferData(flavor));
            if (file != null && !isFalse(callF(onDrop, file)))
              e.dropComplete(true);
            ret;
          }
        }
      }
      e.rejectDrop();
    }
  });
  ret c;
}

static <A extends JComponent> A jHandleFileDrop(IVF1<File> onDrop, A c) {
  ret jHandleFileDrop((O) onDrop, c);
}

static <A extends JComponent> A jHandleFileDrop(O onDrop, A c) {
  ret jHandleFileDrop(c, onDrop);
}

Began life as a copy of #1006013