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COS 381

COS 381. Day 10. Agenda. Assignment 2 Posted Program a web-based Version of Soduku using JavaScript and DOM http://www.soduku.org/ to learn how to play Due Tuesday, February 21 Capstone Proposals will be due soon Start thinking about a project 10% of Capstone grade is Timeliness

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COS 381

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  1. COS 381 Day 10

  2. Agenda • Assignment 2 Posted • Program a web-based Version of Soduku using JavaScript and DOM • http://www.soduku.org/ to learn how to play • Due Tuesday, February 21 • Capstone Proposals will be due soon • Start thinking about a project • 10% of Capstone grade is Timeliness • Today we start on Java Applets • Assumption is that student know about Object-oriented programming (COS 260 is prerequisite ) • Assignment 3 will be posted by next class • Series of Java applets

  3. Setting up for Creating Java Applets • You will need two things (all free!) • The JAVA SDK • Current is J2SE 5.0 • http://java.sun.com/j2se/1.5.0/download.jsp • A development environment • JGRASP << recommended • http://spider.eng.auburn.edu/user-cgi/grasp/grasp.pl?;dl=download_jgrasp.html • NetBeans • Comes with the JAVA SDK • eclipse • http://www.eclipse.org/downloads/

  4. 7.1Introduction - Applets are relatively small Java programs whose execution is triggered by a browser - The purpose of an applet is to provide processing capability and interactivity for HTML documents through widgets - The ‘standard’ operations of applets are provided by the parent class, JApplet public class class_name extends JApplet { … } - Use of applets is still widespread, and there is heavy use in intranets, where all browsers can be required to support the latest JVM - Applets are an alternative to CGI and embedded client-side scripts

  5. 7.1 Introduction (continued) - Comparisons (between JavaScript & applets): - CGI is faster than applets and JavaScript, but it is run on the server - JavaScript is easier to learn and use than Java, but less expressive - Java is faster than JavaScript - Java graphics are powerful, but JavaScript has none - JavaScript does not require the additional download from the server that is required for applets - Java may become more of a server-side tool, in the form of servlets and JSP, than a client-side tool

  6. 7.2 Primary Applet Activities - Browser actions: a. Download and instantiate the applet class b. Call the applet’s init method c. Call the applet’s start method - This starts the execution of the applet - When the user takes a link from the document that has the applet, the browser calls the applet’s stop method - When the browser is stopped by the user, the browser calls the applet’s destroy method - An applet’s display is actually a multi-layered frame - We’re only interested in one layer, the content pane - We don’t write directly to the content pane

  7. 7.2 Primary Applet Activities • Two categories of graphics operations in applets: • 1. Custom drawing – use a set of primitives, using overriden versions of paintComponent • - Custom drawing is done outside the applet, usually in a Jpanel panel • - The applet instantiates the panel and adds it to the applet’s content pane • 2. Use predefined graphics objects • - Do not use paintComponent • - Put graphics objects directly into a panel created in the applet

  8. 7.3 The paintComponent Method (continued) - Always called by the browser (not the applet itself) - Takes one parameter, an object of class Graphics, which is defined in java.awt - The parameter object is created by the browser - The protocol of paintComponent is: public void paintComponent( Graphics grafObj) { … } - The simplest use of paintComponent is to display text, using the drawString method - Three parameters: a String literal, the x coordinate of the left end of the string, and the y coordinate of the base of the string - Before calling drawString (or any other primitive), the parent class’ paintComponent method is called to paint the background super.paintComponent(grafObj);  SHOW Wel.java and Wel.htm

  9. 7.3 The paintComponent Method (continued) - Font Control - The Wel applet draws strings using default values for the font, the font size, and the font style - The Font class, defined in java.awt.Font, has three variables that specify the font name, style, and size of the font used by drawString The size parameter is in points - The styles are PLAIN, BOLD, and ITALIC - To change the font, create a Font object with the desired parameters and set it with the setFont method of Graphics, which takes a Font parameter  SHOW Wel2.java and Wel2.html

  10. 7.4 The <object> Tag - Used to specify an applet in an HTML document - Creates a space in the document display for applet output (like <img> does) <object codetype = "application/java" classid = "java:applet_class_file" width = "applet display width" height = "applet display height"> </object> - The display width and height are in pixels - The applet_class_file is the compiled version - To test the Wel2 applet, we could use <object codetype = "application/java" classid = "java:Wel2.class" width = "500" height = "100"> </object>

  11. 7.4 The <object> Tag (continued) • - Portability problem with the <object> tag: • - <object> is part of the HTML 4.0 standard, but • - IE6 recognizes <object>, but not the classid • attribute (it likes the code attribute, instead) • - If code is used, the java: part must be omitted • - Likewise for appletviewer • - NS6 does not recognize the code attribute

  12. A Better Way <object classid="clsid:CAFEEFAC-0015-0000-0000-ABCDEFFEDCBA“> <param name="code" value="Applet1.class"> <comment> <embed code="Applet1.class" type="application/x-java-applet;jpi-version=1.5.0"> <noembed> No Java Support. </noembed> </embed> </comment> -</object> http://java.sun.com/j2se/1.5.0/docs/guide/plugin/developer_guide/using_tags.html http://ww2.cs.fsu.edu/~steele/XHTML/appletObject.html

  13. An even better way <script language="Javascript"> var _app = navigator.appName; if (_app == 'Netscape') { document.write('<embed code="Applet1.class"', 'width="200"', 'height="200"', 'type="application/x-java-applet;version=1.5.0">'); } else if (_app == 'Microsoft Internet Explorer') { document.write('<OBJECT ', 'classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93"', 'width="200"', 'height="200">', '<PARAM name="code" value="Applet1.class">', '</OBJECT>'); } else { document.write('<p>Sorry, unsupported browser.</p>'); } </script>

  14. xhtml 1.1 and cross browser <body> <p> <!--[if !IE]>--> <object classid="java:Wel2.class" type="application/x-java-applet" height="100" width="500" > <!--<![endif]--> <object classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93" height="100" width="500" > <param name="code" value="Wel2" /> </object> <!--[if !IE]>--> </object> <!--<![endif]--> </p> </body>

  15. 7.5 Applet Parameters - Applets can be sent parameters through HTML, using the <param> tag and its two attributes, name and value - Parameter values are strings - e.g., <param name = "fruit" value = "apple"> - The applet gets the parameter values with getParameter, which takes a string parameter, which is the name of the parameter String myFruit = getParameter("fruit"); - If no parameter with the given name has been specified in the HTML document, getParameter returns null - By checking the return value against null, a default value can be set - If the parameter value is not really a string (although parameters are all sent as strings), the value returned from getParameter must be converted, as on the next page…

  16. 7.5 Applet Parameters (continued) String pString = getParameter("size"); if (pString == null) mySize = 24; else mySize = Integer.parseInt(pString); - The best place to put the code to get parameter values is in init - Parameters are stored in instance variables  SHOWWel3.javaand Wel3.html

  17. COS 381 Day 11

  18. Agenda • Assignment 2 Due • Assignment 3 Posted • Due March 3 • Problem 2, 3 & 6 on pages 294 and 295 • Capstone Proposals will be due on Feb 28 • Start thinking about a project • 10% of Capstone grade is Timeliness • Today >> Java Applets • Assumption is that student know about Object-oriented programming (COS 260 is prerequisite )

  19. AFUM Scholarship • Last year AFUM awarded 3 $500 scholarships • Criteria • UMFK student that will have completed 24 Credits by this spring and is returning to UMFK next fall • Complete a Letter of Commitment to scholarship and service • One Letter of recommendation from a faculty member • A resume • Copy of your transcript (get from registrar) • Turn in all materials to Prof. Stephen Hansen by March 3, 2006 • Room 232 Nadeau Hall

  20. Java in xHtml 1.1 http://perleybrook.umfk.maine.edu/examples/testxhtml.htm

  21. 7.6 Simple Graphics - Coordinate system: (0, 0) is at the upper left corner - The methods that draw graphic figures are called through the Graphics object (the parameter to paintComponent) - Lines are drawn with drawLine(x1, y1, x2, y2) - Draws a line from (x1, y1) to (x2, y2)

  22. 7.6 Simple Graphics (continued) - Rectangles are drawn with drawRect and fillRect - Both take four parameters, the coordinates of the upper left corner of the rectangle and the width and height of the rectangle (width and height are in pixels) - Rectangles with rounded corners can be drawn with drawRoundRect and fillRoundRect - These two take two more parameters, which specify the numbers of horizontal pixels and vertical pixels in the rounding  SHOW Rectangles.javaand Rectangles.html

  23. 7.6 Simple Graphics (AWT) (continued) - 3D rectangles can be created with a 5th parameter, true (not pushed) or false (pushed) - Polygons are drawn with drawPolygon, which takes three parameters, two arrays of coordinates of edge endpoints, and the number of edges  SHOW Polygons.java • drawPolygon can also take a single parameter, which is a Polygon object, whose constructor takes the same three parameters as drawPolygon • - Ovals are like rectangles (same parameters)  SHOWPolygons.java and Polygons.html

  24. 7.7 Color - The Color class has predefined objects for common colors Color.white, Color.black, Color.gray, Color.red, Color.green, Color.blue, Color.yellow, Color.magenta, Color.cyan, Color.pink, Color.orange - An object for any color can be created with the Color constructor, as in Color myColor = new Color(x, y, z); - The color of the Graphics object can be set with setColor, as in grafObj.setColor(Color.cyan); - The foreground and background colors of the applet display are set with methods from JPanel

  25. 7.8 Interactive Applets • Java Swing GUI Components (widgets) • 1. Labels • - JLabel objects are static strings • final JLabel labl1 = new JLabel("Click this button"); • 2. Plain buttons • JButton myButton = new JButton("Click here for fun"); • 3. Checkboxes • JCheckbox box1 = new JCheckbox("Beer"); • JCheckbox box2 = new JCheckbox("Pretzels"); • - JCheckbox can take a second parameter, a Boolean, that specifies the the initial checkness of the box

  26. 7.8 Interactive Applets (continued) 4. Radio buttons – JRadioButton objects in a ButtonGroup ButtonGroup drink = new ButtonGroup(); JRadioButton box1 = new JRadioButton("Coke", true); JRadioButton box2 = new JRadioButton("Pepsi", false); drink.add(box1); drink.add(box2); 5. Text Boxes – JTextField objects JTextField age = new JTextField(3); - Could take a different first parameter, a string literal, which appears in the box when the box is initially displayed

  27. 7.8 Interactive Applets (continued) • - A panel object is needed to contain components • - In this case, the panel can be created in the applet • JPanel myPanel = new JPanel(); • myPanel.setBackground(Color.yellow); • myPanel.setForeground(Color.blue); • myPanel.add(box1); • - Layout Managers • - Default for Swing is BorderLayout – places components on the borders of the panel • - GridLayout is similar to HTML document panels • JPanel buttonPanel = new JPanel(); • buttonPanel.setLayout( • new GridLayout(3, 2, 10, 10)); • - Three rows of two components each, with 10 pixels between the components  SHOWPizza.java and Pizza.html

  28. 7.8 Interactive Applets (continued)

  29. 7.8 Interactive Applets (continued) - The Java Event Model - Related to the JavaScript event model - Event handlers are called event listeners - Connection of an event to a listener is established through event listener registration - Done with a method of the class that implements the listener interface - The panel object that holds the components can be the event listener for those components - Event generators send messages (call methods) to registered event listeners when events occur - Event handling methods must conform to a standard protocol, which comes from an interface - We only consider the “semantic” events (there are also “low-level” events)

  30. 7.8 Interactive Applets (continued) - Semantic Event Classes ActionEventclick a button, select from a menu or list, or type the enter button in a text field ItemEventselect a checkbox or list item TextEventchange the contents of a text field or text area - For the two most commonly used events, ActionEvent and ItemEvent, there are the following interfaces and handler methods: Interface Handler method ActionListener actionPerformed ItemListener itemStateChanged - The methods to register the listener is the interface name with “add” prepended - e.g., button1.addActionListener(this);

  31. 7.8 Interactive Applets (continued) • - Event handlers get an event object as a parameter, through which information about the event can be gotten with methods, such as getState • - e.g., button1.getState() returns true if the button is on, false otherwise • - When an event handler has just a few lines, it can be implemented as an instance of an anonymous nested class • - Example: a button that sets a font • button.addActionListener(new ActionListener(){ • public void actionPerformed(ActionEvent e) { • text.setFont(newFont); • } • }); • SHOW RadioB.java and RadioB.html - Note: It does not use an inner class for the handler

  32. 7.9 Concurrency in Java - Our only interest in concurrency here is to illustrate how threads can be used to create animation in an applet - A thread of control is a sequence of program points reached as execution flows through the program - A nonconcurrent program has a single thread of control; a concurrent program has more than one - Java supports lightweight concurrency through its threads - The concurrent program units in Java are methods named run, whose code can be in concurrent execution with other run methods and with main - There are two ways to implement threads, as a subclass of Thread and by implementing the interface Runnable - The Thread class - Two essential methods, run and start - run is the concurrent method - start tells the run method to begin execution

  33. 7.9 Concurrency in Java (continued) - All Java programs run in threads - For applications, when execution is to begin, a thread is created for main and its start method is called - For applets, when the browser finds one, it creates a thread and calls the applet --> SHOWNames.java, output, delayer, and output - Thread States - New - created, but start hasn’t been called - Runnable or ready - ready to run, but is not currently running - In the ready queue - Running - actually has the processor - Blocked - was running, but is not now, because it was interrupted (i/o, end of time slot, gave up its time slot, etc.) - Dead - either its stop was called or its run method completed its execution

  34. 7.9 Concurrency in Java (continued) - Thread methods - yield is a request from the running thread to give up the processor; a static method - sleep(time) - blocks the thread for at least as many milliseconds as the parameter specifies; also a static method - sleep can throw InterruptedException, which must be caught - stop - now deprecated, because of safety problems - Now we override it and just set the thread reference to null (destroys the thread) - An example - an animated digital clock - An applet must implement Runnable, its start and stop methods, and the repaint method of Graphics - repaint is called after the applet display has changed

  35. 7.9 Concurrency in Java (continued) - Our applet is named Clock - Its start method creates a new Thread object, sending this to the constructor. This sets the new Thread object’s target to the Clock object, which forces the thread to get its run method from the Clock object - After creating the Thread object, start is called to start its execution - The run method sets a variable to the currently executing thread, and then loops as long as the thread is clockThread - The loop gets the new time with a new Date object and repaints the display every second Clock.java http://perleybrook.umfk.maine.edu/examples/Clock.html

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