Drog and Drop 拖放問題

为什么不能拖放...?哪里出错?
import java.awt.*;
import java.awt.dnd.*;
import java.awt.datatransfer.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.*;public class DragTest extends JFrame implements DragSourceListener, DragGestureListener {  DragSource ds;
  JTable table;
  StringSelection transferable;
  String []col = {"A","B","C","D","E"};
  String [][]items = { {"A","C","D","E","F"},
{"","","","",""},
{"","","","",""},
{"","","","",""},
{"","","","",""},
{"","","","",""},
{"","","","",""},
{"","","","",""},
{"","","","",""},};  public DragTest() {
    super("Drag Test");
    setSize(400,300);
    addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent we) {
        System.exit(0);
      }
    });
table = new JTable(items, col);
table.setColumnSelectionAllowed(true);
table.setRowSelectionAllowed(true);

    getContentPane().add(new JScrollPane(table), BorderLayout.CENTER);    ds = new DragSource();
    DragGestureRecognizer dgr = ds.createDefaultDragGestureRecognizer(
  table, DnDConstants.ACTION_MOVE, this);
    setVisible(true);
  }  public void dragGestureRecognized(DragGestureEvent dge) {
    System.out.println("Drag Gesture Recognized!");
    transferable = new StringSelection((table.getValueAt(table.getSelectedRow(), table.getSelectedColumn())).toString());
    ds.startDrag(dge, DragSource.DefaultCopyDrop, transferable, this);
  }  public void dragEnter(DragSourceDragEvent dsde) {
    System.out.println("Drag Enter");
  }  public void dragExit(DragSourceEvent dse) {
    System.out.println("Drag Exit");
  }  public void dragOver(DragSourceDragEvent dsde) {
    System.out.println("Drag Over");
  }  public void dragDropEnd(DragSourceDropEvent dsde) {
    System.out.print("Drag Drop End: ");
    if (dsde.getDropSuccess()) {
      System.out.println("Succeeded");
    }
    else {
      System.out.println("Failed");
    }
  }  public void dropActionChanged(DragSourceDragEvent dsde) {
    System.out.println("Drop Action Changed");
  }  public static void main(String args[]) {
    new DragTest();
  }
}