求助java Toolkit.getDefaultToolkit().creatImage(String filename)

7875405 2016-04-08 01:48:47

java.awr.Image是个抽象类，不可实例化。Image对象一般由如下方法得到。
Image image= Toolkit.getDefaultToolkit().creatImage(String filename)获得。查看了源码

public static synchronized Toolkit getDefaultToolkit()返回一个单例的Toolkit，
而Toolkit类中的createImage（）是抽象的。

public abstract Image createImage(String filename);
并没有函数体，是一个抽象函数。
搞不懂这个image是怎样通过createImage（）创建的。

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多媒体编程 Java程序设计多媒体编程全文共8页，当前为第1页。多媒体编程一、加载和显示图像 1.对于Application程序：使用Toolkit类提供的方法： Image getImage(URL url); Image getImage(String filename); 2.得到Toolkit对象的两种方法：一、类Toolit的静态方法：getDefaultToolkit() 二、调用某个组件对象的实例方法getToolkit() 例： Image imageObj=Toolkit.getDefaultToolkit().getImage("fileObj.gif"); Image imageObj=getToolkit().getImage("fileObj.gif"); 多媒体编程全文共8页，当前为第2页。示例说明： (1)类Applet中提供了getImage()，可以直接载入图像，方法格式如下： Image getImage(URL url) Image getImage(URL url,String name); 第一种方法要指明图像文件的绝对URL地址

实现文件的拖拽功能 import java.awt.AlphaComposite; import java.awt.Component; import java.awt.Graphics2D; import java.awt.Point; import java.awt.Rectangle; import java.awt.Toolkit; import java.awt.datatransfer.DataFlavor; import java.awt.datatransfer.StringSelection; import java.awt.datatransfer.Transferable; import java.awt.datatransfer.UnsupportedFlavorException; import java.awt.dnd.DnDConstants; import java.awt.dnd.DragGestureEvent; import java.awt.dnd.DragGestureListener; import java.awt.dnd.DragSource; import java.awt.dnd.DragSourceDragEvent; import java.awt.dnd.DragSourceDropEvent; import java.awt.dnd.DragSourceEvent; import java.awt.dnd.DragSourceListener; 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; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.KeyAdapter; import java.awt.event.KeyEvent; import java.awt.geom.AffineTransform; import java.awt.geom.Rectangle2D; import java.awt.image.BufferedImage; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.util.Iterator; import java.util.List; import javax.swing.Icon; import javax.swing.JLabel; import javax.swing.JTree; import javax.swing.Timer; import javax.swing.event.TreeExpansionEvent; import javax.swing.event.TreeExpansionListener; import javax.swing.filechooser.FileSystemView; import javax.swing.tree.DefaultMutableTreeNode; import javax.swing.tree.DefaultTreeCellRenderer; import javax.swing.tree.DefaultTreeModel; import javax.swing.tree.TreePath; class DragTree extends JTree implements DragGestureListener, DragSourceListener, DropTargetListener { /** * */ private static final long serialVersionUID = 1L; BufferedImage ghostImage; private Rectangle2D ghostRect = new Rectangle2D.Float(); private Point ptOffset = new Point(); private Point lastPoint = new Point(); private TreePath lastPath; private Timer hoverTimer; FileNode sourceNode; public DragTree() { DragSource dragSource = DragSource.getDefaultDragSource(); dragSource.createDefaultDragGestureRecognizer(this, // component where // drag originates DnDConstants.ACTION_COPY_OR_MOVE, // actions this); // drag gesture recognizer setModel(createTreeModel()); addTreeExpansionListener(new TreeExpansionListener() { public void treeCollapsed(TreeExpansionEvent e) { } public void treeExpanded(TreeExpansionEvent e) { TreePath path = e.getPath(); if (path != null) { FileNode node = (FileNode) path.getLastPathComponent(); if (!node.isExplored()) { DefaultTreeModel model = (DefaultTreeModel) getModel(); node.explore(); model.nodeStructureChanged(node); } } } }); this.setCellRenderer(new DefaultTreeCellRenderer() { public Component getTreeCellRendererComponent(JTree tree, Object value, boolean selected, boolean expanded, boolean leaf, int row, boolean hasFocus) { TreePath tp = tree.getPathForRow(row); if (tp != null) { FileNode node = (FileNode) tp.getLastPathComponent(); File f = node.getFile(); try { Icon icon = FileSystemView.getFileSystemView() .getSystemIcon(f); this.setIcon(icon); this.setLeafIcon(icon); this.setOpenIcon(icon); this.setClosedIcon(icon); this.setDisabledIcon(icon); } catch (Exception e) { e.printStackTrace(); } } return super.getTreeCellRendererComponent(tree, value, selected, expanded, leaf, row, hasFocus); } }); super.setScrollsOnExpand(true); new DropTarget(this, DnDConstants.ACTION_COPY_OR_MOVE, this); // Set up a hover timer, so that a node will be automatically expanded // or collapsed // if the user lingers on it for more than a short time hoverTimer = new Timer(1000, new ActionListener() { public void actionPerformed(ActionEvent e) { if (lastPath == null) { return; } if (getRowForPath(lastPath) == 0) return; // Do nothing if we are hovering over the root node if (isExpanded(lastPath)) collapsePath(lastPath); else expandPath(lastPath); } }); hoverTimer.setRepeats(false); // Set timer to one-shot mode this.addKeyListener(new KeyAdapter() { public void keyPressed(KeyEvent e) { int code = e.getKeyCode(); int modifiers = e.getModifiers(); if (code == 'v' || code == 'V') { System.out.println("find v"); System.out.println("modifiers:" + modifiers + "\t" + ((modifiers & KeyEvent.CTRL_MASK) != 0)); } if ((modifiers & KeyEvent.CTRL_MASK) != 0 && (code == 'v' || code == 'V')) { Transferable tr = Toolkit.getDefaultToolkit() .getSystemClipboard().getContents(null); TreePath path = getSelectionPath(); if (path == null) { return; } FileNode node = (FileNode) path.getLastPathComponent(); if (node.isDirectory()) { System.out.println("file cp"); try { List list = (List) (tr .getTransferData(DataFlavor.javaFileListFlavor)); Iterator iterator = list.iterator(); File parent = node.getFile(); while (iterator.hasNext()) { File f = (File) iterator.next(); cp(f, new File(parent, f.getName())); } node.reexplore(); } catch (Exception ioe) { ioe.printStackTrace(); } updateUI(); } } } }); } public void dragGestureRecognized(DragGestureEvent e) { // drag anything ... TreePath path = getLeadSelectionPath(); if (path == null) return; FileNode node = (FileNode) path.getLastPathComponent(); sourceNode = node; // Work out the offset of the drag point from the TreePath bounding // rectangle origin Rectangle raPath = getPathBounds(path); Point ptDragOrigin = e.getDragOrigin(); ptOffset.setLocation(ptDragOrigin.x - raPath.x, ptDragOrigin.y - raPath.y); // Get the cell renderer (which is a JLabel) for the path being dragged int row = this.getRowForLocation(ptDragOrigin.x, ptDragOrigin.y); JLabel lbl = (JLabel) getCellRenderer().getTreeCellRendererComponent( this, // tree path.getLastPathComponent(), // value false, // isSelected (dont want a colored background) isExpanded(path), // isExpanded getModel().isLeaf(path.getLastPathComponent()), // isLeaf row, // row (not important for rendering) false // hasFocus (dont want a focus rectangle) ); lbl.setSize((int) raPath.getWidth(), (int) raPath.getHeight()); // <-- // The // layout // manager // would // normally // do // this // Get a buffered image of the selection for dragging a ghost image this.ghostImage = new BufferedImage((int) raPath.getWidth(), (int) raPath.getHeight(), BufferedImage.TYPE_INT_ARGB_PRE); Graphics2D g2 = ghostImage.createGraphics(); // Ask the cell renderer to paint itself into the BufferedImage g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC, 0.5f)); // Make the image ghostlike lbl.paint(g2); g2.dispose(); // this.getGraphics().drawImage(ghostImage, e.getDragOrigin().x, // e.getDragOrigin().y, this); e.startDrag( null, // cursor ghostImage, new Point(5, 5), new StringSelection(getFilename()), // transferable this); // drag source listener } public void dragDropEnd(DragSourceDropEvent e) { ghostImage = null; sourceNode = null; } public void dragEnter(DragSourceDragEvent e) { } public void dragExit(DragSourceEvent e) { if (!DragSource.isDragImageSupported()) { repaint(ghostRect.getBounds()); } } public void dragOver(DragSourceDragEvent e) { } public void dropActionChanged(DragSourceDragEvent e) { } public String getFilename() { TreePath path = getLeadSelectionPath(); FileNode node = (FileNode) path.getLastPathComponent(); return ((File) node.getUserObject()).getAbsolutePath(); } private DefaultTreeModel createTreeModel() { File root = FileSystemView.getFileSystemView().getRoots()[0]; FileNode rootNode = new FileNode(root); rootNode.explore(); return new DefaultTreeModel(rootNode); } public void dragEnter(DropTargetDragEvent dtde) { } public void dragOver(DropTargetDragEvent dtde) { Point pt = dtde.getLocation(); if (pt.equals(lastPoint)) { return; } if (ghostImage != null) { Graphics2D g2 = (Graphics2D) getGraphics(); // If a drag image is not supported by the platform, then draw my // own drag image if (!DragSource.isDragImageSupported()) { paintImmediately(ghostRect.getBounds()); // Rub out the last // ghost image and cue // line // And remember where we are about to draw the new ghost image ghostRect.setRect(pt.x - ptOffset.x, pt.y - ptOffset.y, ghostImage.getWidth(), ghostImage.getHeight()); g2.drawImage((ghostImage), AffineTransform .getTranslateInstance(ghostRect.getX(), ghostRect.getY()), null); } } TreePath path = getClosestPathForLocation(pt.x, pt.y); if (!(path == lastPath)) { lastPath = path; hoverTimer.restart(); } } public void dropActionChanged(DropTargetDragEvent dtde) { } public void drop(DropTargetDropEvent e) { try { DataFlavor stringFlavor = DataFlavor.stringFlavor; Transferable tr = e.getTransferable(); TreePath path = this.getPathForLocation(e.getLocation().x, e.getLocation().y); if (path == null) { e.rejectDrop(); return; } FileNode node = (FileNode) path.getLastPathComponent(); if (e.isDataFlavorSupported(DataFlavor.javaFileListFlavor) && node.isDirectory()) { e.acceptDrop(DnDConstants.ACTION_COPY_OR_MOVE); System.out.println("file cp"); List list = (List) (e.getTransferable() .getTransferData(DataFlavor.javaFileListFlavor)); Iterator iterator = list.iterator(); File parent = node.getFile(); while (iterator.hasNext()) { File f = (File) iterator.next(); cp(f, new File(parent, f.getName())); } node.reexplore(); e.dropComplete(true); this.updateUI(); } else if (e.isDataFlavorSupported(stringFlavor) && node.isDirectory()) { String filename = (String) tr.getTransferData(stringFlavor); if (filename.endsWith(".txt") || filename.endsWith(".java") || filename.endsWith(".jsp") || filename.endsWith(".html") || filename.endsWith(".htm")) { e.acceptDrop(DnDConstants.ACTION_COPY_OR_MOVE); File f = new File(filename); if (f.exists()) { f.renameTo(new File(node.getFile(), f.getName())); node.reexplore(); ((FileNode) sourceNode.getParent()).remove(sourceNode); e.dropComplete(true); this.updateUI(); } else { e.rejectDrop(); } } else { e.rejectDrop(); } } else { e.rejectDrop(); } } catch (IOException ioe) { ioe.printStackTrace(); } catch (UnsupportedFlavorException ufe) { ufe.printStackTrace(); } finally { ghostImage = null; this.repaint(); } } private void cp(File src, File dest) throws IOException { if (src.isDirectory()) { if (!dest.exists()) { boolean ret = dest.mkdir(); if (ret == false) return; } File[] fs = src.listFiles(); for (int i = 0; i < fs.length; i++) { cp(fs[i], new File(dest, fs[i].getName())); } return; } byte[] buf = new byte[1024]; FileInputStream in = new FileInputStream(src); FileOutputStream out = new FileOutputStream(dest); int len; try { while ((len = in.read(buf)) > 0) { out.write(buf, 0, len); } } finally { in.close(); out.close(); } } public void dragExit(DropTargetEvent dte) { } } class FileNode extends DefaultMutableTreeNode { private boolean explored = false; public FileNode(File file) { setUserObject(file); } public boolean getAllowsChildren() { return isDirectory(); } public boolean isLeaf() { return !isDirectory(); } public File getFile() { return (File) getUserObject(); } public boolean isExplored() { return explored; } public boolean isDirectory() { File file = getFile(); return file.isDirectory(); } public String toString() { File file = (File) getUserObject(); String filename = file.toString(); int index = filename.lastIndexOf(File.separator); return (index != -1 && index != filename.length() - 1) ? filename .substring(index + 1) : filename; } public void explore() { if (!isDirectory()) return; if (!isExplored()) { File file = getFile(); File[] children = file.listFiles(); for (int i = 0; i < children.length; ++i) { if (children[i].isDirectory()) add(new FileNode(children[i])); } for (int i = 0; i < children.length; ++i) { if (!children[i].isDirectory()) add(new FileNode(children[i])); } explored = true; } } public void reexplore() { this.removeAllChildren(); explored = false; explore(); } }

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