Αντικειμενοστραφής Προγραμματισμός

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====== TreeDemo ======

Για την ορθή εκτέλεση του παρακάτω παραδείγματος θα χρειαστείτε και αυτά τα αρχεία html {{:swing:html.zip|}}.

<code java TreeDemo.java>
package components;
/**
 * This application that requires the following additional files:
 *   TreeDemoHelp.html
 *  arnold.html
 *  bloch.html
 *  chan.html
 *  jls.html
 *  swingtutorial.html
 *  tutorial.html
 *  tutorialcont.html
 *  vm.html
 */
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JSplitPane;
import javax.swing.UIManager;

import javax.swing.JTree;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreeSelectionModel;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.event.*;

import java.net.URL;
import java.io.IOException;
import java.awt.Dimension;
import java.awt.GridLayout;

public class TreeDemo extends JPanel
            implements TreeSelectionListener {
  private JEditorPane htmlPane;
  private JTree tree;
  private URL helpURL;
  private static boolean DEBUG = false;

  //Optionally play with line styles.  Possible values are
  //"Angled" (the default), "Horizontal", and "None".
  private static boolean playWithLineStyle = false;
  private static String lineStyle = "Horizontal";
  
  //Optionally set the look and feel.
  private static boolean useSystemLookAndFeel = false;

  public TreeDemo() {
    super(new GridLayout(1,0));

    //Create the nodes.
    DefaultMutableTreeNode top =
      new DefaultMutableTreeNode("The Java Series");
    createNodes(top);

    //Create a tree that allows one selection at a time.
    tree = new JTree(top);
    tree.setEditable(true);
    tree.getSelectionModel().setSelectionMode
        (TreeSelectionModel.SINGLE_TREE_SELECTION);

    //Listen for when the selection changes.
    tree.addTreeSelectionListener(this);

    if (playWithLineStyle) {
      System.out.println("line style = " + lineStyle);
      tree.putClientProperty("JTree.lineStyle", lineStyle);
    }

    //Create the scroll pane and add the tree to it. 
    JScrollPane treeView = new JScrollPane(tree);

    //Create the HTML viewing pane.
    htmlPane = new JEditorPane();
    htmlPane.setEditable(false);
    initHelp();
    JScrollPane htmlView = new JScrollPane(htmlPane);

    //Add the scroll panes to a split pane.
    JSplitPane splitPane = new JSplitPane(JSplitPane.VERTICAL_SPLIT);
    splitPane.setTopComponent(treeView);
    splitPane.setBottomComponent(htmlView);

    Dimension minimumSize = new Dimension(100, 50);
    htmlView.setMinimumSize(minimumSize);
    treeView.setMinimumSize(minimumSize);
    splitPane.setDividerLocation(100); 
    splitPane.setPreferredSize(new Dimension(500, 300));

    //Add the split pane to this panel.
    add(splitPane);
  }

  /** Required by TreeSelectionListener interface. */
  public void valueChanged(TreeSelectionEvent e) {
    DefaultMutableTreeNode node = (DefaultMutableTreeNode)
               tree.getLastSelectedPathComponent();

    if (node == null) return;

    Object nodeInfo = node.getUserObject();
    if (node.isLeaf()) {
      BookInfo book = (BookInfo)nodeInfo;
      displayURL(book.bookURL);
      if (DEBUG) {
        System.out.print(book.bookURL + ":  \n  ");
      }
    } else {
      displayURL(helpURL); 
    }
    if (DEBUG) {
      System.out.println(nodeInfo.toString());
    }
  }

  private class BookInfo {
    public String bookName;
    public URL bookURL;

    public BookInfo(String book, String filename) {
      bookName = book;
      bookURL = getClass().getResource("html/"+filename);
      if (bookURL == null) {
        System.err.println("Couldn't find file: "
                   + filename);
      }
    }

    public String toString() {
      return bookName;
    }
  }

  private void initHelp() {
    String s = "TreeDemoHelp.html";
    helpURL = getClass().getResource(s);
    if (helpURL == null) {
      System.err.println("Couldn't open help file: " + s);
    } else if (DEBUG) {
      System.out.println("Help URL is " + helpURL);
    }

    displayURL(helpURL);
  }

  private void displayURL(URL url) {
    try {
      if (url != null) {
        htmlPane.setPage(url);
      } else { //null url
		htmlPane.setText("File Not Found");
        if (DEBUG) {
          System.out.println("Attempted to display a null URL.");
        }
      }
    } catch (IOException e) {
      System.err.println("Attempted to read a bad URL: " + url);
    }
  }

  private void createNodes(DefaultMutableTreeNode top) {
    DefaultMutableTreeNode category = null;
    DefaultMutableTreeNode book = null;

    category = new DefaultMutableTreeNode("Books for Java Programmers");
    top.add(category);

    //original Tutorial
    book = new DefaultMutableTreeNode(new BookInfo
      ("The Java Tutorial: A Short Course on the Basics",
      "tutorial.html"));
    category.add(book);

    //Tutorial Continued
    book = new DefaultMutableTreeNode(new BookInfo
      ("The Java Tutorial Continued: The Rest of the JDK",
      "tutorialcont.html"));
    category.add(book);

    //JFC Swing Tutorial
    book = new DefaultMutableTreeNode(new BookInfo
      ("The JFC Swing Tutorial: A Guide to Constructing GUIs",
      "swingtutorial.html"));
    category.add(book);

    //Bloch
    book = new DefaultMutableTreeNode(new BookInfo
      ("Effective Java Programming Language Guide",
	   "bloch.html"));
    category.add(book);

    //Arnold/Gosling
    book = new DefaultMutableTreeNode(new BookInfo
      ("The Java Programming Language", "arnold.html"));
    category.add(book);

    //Chan
    book = new DefaultMutableTreeNode(new BookInfo
      ("The Java Developers Almanac",
       "chan.html"));
    category.add(book);

    category = new DefaultMutableTreeNode("Books for Java Implementers");
    top.add(category);

    //VM
    book = new DefaultMutableTreeNode(new BookInfo
      ("The Java Virtual Machine Specification",
       "vm.html"));
    category.add(book);

    //Language Spec
    book = new DefaultMutableTreeNode(new BookInfo
      ("The Java Language Specification",
       "jls.html"));
    category.add(book);
  }
    
  /**
   * Create the GUI and show it.  For thread safety,
   * this method should be invoked from the
   * event dispatch thread.
   */
  private static void createAndShowGUI() {
    if (useSystemLookAndFeel) {
      try {
        UIManager.setLookAndFeel(
          UIManager.getSystemLookAndFeelClassName());
      } catch (Exception e) {
        System.err.println("Couldn't use system look and feel.");
      }
    }

    //Create and set up the window.
    JFrame frame = new JFrame("TreeDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Add content to the window.
    frame.add(new TreeDemo());

    //Display the window.
    frame.pack();
    frame.setVisible(true);
  }

  public static void main(String[] args) {
    //Schedule a job for the event dispatch thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        createAndShowGUI();
      }
    });
  }
}
</code>