The Code - Java

Find below a complete listing of the code in our class. Have a quick look at it now, but don’t worry if you don’t understand all the details. Some basic knowledge of Java is assumed so not all the lines of code will be discussed. Relevant sections will be explained in detail.

   1://////////////////////////////////////////////////////////////////
   2:/**
   3:* This class creates a frame with a JEditorPane for loading HTML
   4:* help files
   5:*/
   6://package goes here
   7:import java.io.*;
   8:import javax.swing.event.*;
   9:import javax.swing.*;
  10:import java.net.*;
  11:import java.awt.event.*;
  12:import java.awt.*;
  13:
  14:public class HelpWindow extends JFrame implements ActionListener{
  15:    private final int WIDTH = 600;
  16:    private final int HEIGHT = 400;
  17:    private JEditorPane editorpane;
  18:    private URL helpURL;
  19://////////////////////////////////////////////////////////////////
  20:/**
  21: * HelpWindow constructor
  22: * @param String and URL
  23: */
  24:public HelpWindow(String title, URL hlpURL) {
  25:    super(title);
  26:    helpURL = hlpURL; 
  27:    editorpane = new JEditorPane();
  28:    editorpane.setEditable(false);
  29:    try {
  30:        editorpane.setPage(helpURL);
  31:    } catch (Exception ex) {
  32:        ex.printStackTrace();
  33:    }
  34:    //anonymous inner listener
  35:    editorpane.addHyperlinkListener(new HyperlinkListener() {
  36:        public void hyperlinkUpdate(HyperlinkEvent ev) {
  37:            try {
  38:                if (ev.getEventType() == HyperlinkEvent.EventType.ACTIVATED) {
  39:                    editorpane.setPage(ev.getURL());
  40:                }
  41:            } catch (IOException ex) {
  42:                //put message in window
  43:                ex.printStackTrace();
  44:            }
  45:        }
  46:    });
  47:    getContentPane().add(new JScrollPane(editorpane));
  48:    addButtons();
  49:    // no need for listener just dispose
  50:    setDefaultCloseOperation(DISPOSE_ON_CLOSE);
  51:    // dynamically set location
  52:    calculateLocation();
  53:    setVisible(true);
  54:    // end constructor
  55:}
  56:/**
  57: * An Actionlistener so must implement this method
  58: *
  59: */
  60:public void actionPerformed(ActionEvent e) {
  61:    String strAction = e.getActionCommand();
  62:    URL tempURL;
  63:    try {
  64:        if (strAction == "Contents") {
  65:            tempURL = editorpane.getPage();
  66:            editorpane.setPage(helpURL);
  67:        }
  68:        if (strAction == "Close") {
  69:            // more portable if delegated
  70:            processWindowEvent(new WindowEvent(this,
  71:                WindowEvent.WINDOW_CLOSING));
  72:        }
  73:    } catch (IOException ex) {
  74:        ex.printStackTrace();
  75:    }
  76:}
  77:/**
  78: * add buttons at the south
  79: */
  80:private void addButtons() {
  81:    JButton btncontents = new JButton("Contents");
  82:    btncontents.addActionListener(this);
  83:    JButton btnclose = new JButton("Close");
  84:    btnclose.addActionListener(this);
  85:    //put into JPanel
  86:    JPanel panebuttons = new JPanel();
  87:    panebuttons.add(btncontents);
  88:    panebuttons.add(btnclose);
  89:    //add panel south
  90:    getContentPane().add(panebuttons, BorderLayout.SOUTH);
  91:}
  92:/**
  93: * locate in middle of screen
  94: */
  95:private void calculateLocation() {
  96:    Dimension screendim = Toolkit.getDefaultToolkit().getScreenSize();
  97:    setSize(new Dimension(WIDTH, HEIGHT));
  98:    int locationx = (screendim.width - WIDTH) / 2;
  99:    int locationy = (screendim.height - HEIGHT) / 2;
100:    setLocation(locationx, locationy);
101:}
102:public static void main(String [] args){  
 103:    URL index = ClassLoader.getSystemResource("index.html");
104:    new HelpWindow("Test", index);
105:
106:}
107:}//end HelpWindow class
108:////////////////////////////////////////////////////////////////