问答题

本题的功能是监听鼠标的拖曳操作。窗口中有一个列表框，列表框中列出了当前目录的所有文件．鼠标选中一个或多个文件后拖曳出窗口，此操作的功能是将拖曳的文件复制一份在拖曳的目的目录下。 import java.awt.*; import java.awt.datatransfer.*; import java.awt.dnd.*; import java.awt.event.*; import java.io.*; import java.util.*; import javax.swing.*; public class java3 { public static void main(String[] args) { JFrame frame=new DragSourceFrame(); frame.setDefaultClose()peration(JFrame.EXITON_CLOSE); frame.show(); } } class DragSourceFrame extends JFrame { public DragSourceFrame() { setTitle("java3"); setSize(WIDTH,HEIGHT); Comainer contentPane=getContentPane(); File f=new File(".").getabsoluteFile(); File[] files=f.listFiles(); model=new DefaultListModel(); for(int i=0;i＜files.length();i++) try { model.addElement(files[i].getCanonicalFile()); } catch (IOException exception) { JOptionPane.showMessageDialog(this,excep-tion); } fileList=new JList(model); contentPane.add(new JScrolIPane(fileList), BorderLayout.CENTER); contentPane.add (new JLabel("从列表中拖曳出文件"), BorderLayout.NORTH); DragSource dragSource=DragSource.getDefault-DragSource(); dragSource.createDefaultDragGestureRecognizer(fileList, DnDConstants.ACTION _ COPY _ OR _MOVE,new DragGestureListener() { public void dragGestureRecognized( DragGestureEvent event) draggedValues = fileList.getSelectedValues(); Transferable transferable =new FileListTransferable(draggedValues); event.startDrag(null,transferable, new FileListDragSourceListener()); } }); } private class FileListDragSourceListener implements DragSourceAdapter public void dragDropEnd( DragSourceDropEvent event) { if (event.getDropSuccess()) { int action=event.getDropAction(); if(action==DnDConstants.ACTION_MOVE) { for(int i=O;i＜draggedValues.length;i++) model.removeElement(draggedValues[i]); } } } } private JList fileList; private DefaultListModel model; private Object[] draggedValues; private static final int WIDTH=300; private static final int HEIGHT=200; } class FileListTransferable implements Transferable { public FileListTransferable(()bject[] files) { fileList=new ArrayList(Arrays.asList(files)); } public DataFlavor[]getTransferDataFlavors() { return flavors; } public boolean isDataFlavorSupported(DataFlavorflavor) { return Arrays.asList(flavors).contains(flavor); } public Object getTransferData(DataFlavor flavor)throws UnsupportedFlavorException { if(flavor.equals(DataFlavor.javaFileListFlavor)return fileList; else if(flavor.equals(DataFlavor.stringFlavor)) return fileList.toString(); else throw new UnsupportedFlavorException(flavor); } private static DataFlavor[]flavors= { DataFlavor.javaFileListFlavor, DataFlavor.stringFlavor }; private java.util.List fileList; }