Java Applet

Introductions Applet is java program that can be embedded into HTML pages Java applets runs on the java enables web browsers such as mozila and internet explorer. Applet is designed to run remotely on the client browser, so there are some restrictions on it. Applet can't access system resources on the local computer. Applets are used to make the web site more dynamic and entertaining.

Advantages of Applet * Applets are cross platform and can run on Windows, Mac OS and Linux platform * Applets can work all the version of Java Plugin * Applets runs in a sandbox, so the user does not need to trust the code, so it can work without security approval * Applets are supported by most web browsers * Applets are cached in most web browsers, so will be quick to load when returning to a web page * User can also have full access to the machine if user allows

Disadvantages of Java Applet * Java plug-in is required to run applet * Java applet requires JVM so first time it takes significant startup time * If applet is not already cached in the machine, it will be downloaded from internet and will take time * Its difficult to desing and build good user interface in applets compared to HTML technology

The Applet class To create an applet, you must import the Applet class This class is in the java.applet package The Applet class contains code that works with a browser to create a display window Capitalization matters! applet and Applet are different names

Importing the Applet class Here is the directive that you need: import java.applet.Applet; import is a keyword java.applet is the name of the package A dot (. ) separates the package from the class Applet is the name of the class There is a semicolon ( ; ) at the end

Applet versus Application Applets are small programs while applications are larger programs. Applets don't have the main method while in an application execution starts with the main method. Applets can run in our browser's window or in an appletviewer. To run the applet in an appletviewer will be an advantage for debugging. Applets are designed for the client site programming purpose while the applications don't have such type of criteria.

The Life cycle of An Applet init(): This method is called to initialized an applet start(): This method is called after the initialization of the applet. stop(): This method can be called multiple times in the life cycle of an Applet. destroy(): This method is called only once in the life cycle of the applet when applet is destroyed.

The Life cycle of An Applet import java.awt.*; import java.applet.*; class Myclass extends Applet{ public void init(){} Publicvoidstart(){} public void stop() {} public void destroy() {} public void paint(Graphics g) {}

Applet Tag [ [ ] [ ].. [alternateHTML] [ ]

Creating First Applet Example import java.applet.*; import java.awt.*; public class FirstApplet extends Applet{ public void paint(Graphics g){ g.drawString("Welcome in Java Applet.",40,20); }

HTML code

Drawing Shapes Example in java Graphics.drawLine() : to draw the line in the applet. drawLine(int X_from_coordinate, int Y_from_coordinate, int X_to_coordinate, int Y_to_coordinate); Graphics.drawString() : draws the given string as the parameter drawString(String string, int X_coordinate, int Y_coordinate); Graphics.drawOval() : draws the circle g.drawOval(int X_coordinate, int Y_coordinate, int Wdth, int height); Graphics.drawRect() : draws the rectangle. Here is the syntax of the drawRect() method : g.drawRect(int X_coordinate, int Y_coordinate, int Wdth, int height)

Drawing Shapes Example using color in java Graphics.setColor() : sets the color for the object by specified color. setColor(Color.color_name); Graphics.fillOval() : to fill the color inside the oval by specified color g.fillColor(Color.color_name); Graphics.fillRect() :to fill the color inside the rectangle by specified color g.fillRect(int X_coordinate, int Y_coordinate, int Wdth, int height)

Passing Parameter in Java Applet The param tag( ) is used to pass the parameters to an applet To access values String strParameter = this.getParameter("Message");

Event Listeners Example To handle the events generated by these buttons you add action listeners e.g. object_name.addActionListener(this);. When the action event occurs, that object's actionPerformed method is invoked. actionPerformed(ActionEvent e)

Display image paint(Graphics g) has used MediaTracker is a utility class that tracks the status of a number of media objects img - image name type of Image. x - lower X - Coordinate type of int. y - lower Y - Coordinate type of int. x1 - upper X - Coordinate type of int. y1 - upper Y - Coordinate type of int.

Java Swing Tutorial

Java Swing * A part of The JFC * Swing Java consists of Look and feel Accessibility Java 2D Drag and Drop, etc

Introductions Swing is one of the Graphical User Interface tool. Swing is used to develop the graphical user interface (GUI) in java. Swing components used for the building of GUI. Swing components are helpful for interactivity to Java applications. The components of Swing toolkit are given below: list controls buttons labels tree controls table controls

Java Swing Class Hierarchy

Swing Events event source // The Event source is the object. It generates Events. event object // The Event object encapsulates the condition changes in the event source. event listener // The Event listener is the object that requests to be notified Event source: Object is handling an event to the event listener.Event handling in Swing toolkit is very easy to handle and powerful. Objects are notified when a specific event occurs.

JFrame Open frame place the icon on the title bar.Methods are as follows: frame.setIconImage(Toolkit.getDefaultToolkit().getI mage("icon_confused.gif")); it’s using the Image class method named getImage().frame.getDefaultToolkit(): //This is the method of the Toolkit class which gets the default toolkit.

createAndShowGUI private static void createAndShowGUI() { //Create and set up the window. JFrame frame = new JFrame("Hi.."); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //Add a label. JLabel label = new JLabel("Hello World"); frame.getContentPane().add(label); //Display the window. frame.pack(); frame.setVisible(true); }

Menus JMenuBar JMenu JMenuItem

checkBox import javax.swing.*; JCheckBox chk = new JCheckBox("This is the Check Box"); frame.add(chk);

Text Area import javax.swing.JTextArea; // Create a text area with some initial text JTextArea textarea = new JTextArea("Initial Text"); int rows = 20; int cols = 30; textarea = new JTextArea("Initial Text", rows, cols); TextField JTextField t = new JTextField("Text field 3", 8);

JButton Button: Two types: JButton(), JButton(Name) JButton () is used for create blank JButton instance. JButton (Name) is used for create a JButton instance with the specified text. JButton Button1; Button1 = new JButton ("Black is White"); add (Button1);

Layout Managers Most Swing UIs utilise a LayoutManager to control positioning of items There is a choice of these which work in different ways Initially we do without one, and position items ourselves: frame.setLayout(null);

Absolute positioning JFrame frame = new JFrame("I am a JFrame"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(20,30,300,100); frame.setLayout(null); JButton butt=new JButton("Click me"); frame.getContentPane().add(butt); butt.setBounds(20, 20, 200,20); frame.setVisible(true);

FlowLayout JFrame.setDefaultLookAndFeelDecorated(true); JFrame frame = new JFrame("FlowLayout"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.getContentPane().setLayout(new FlowLayout()); JButton b1 = new JButton("Hello"); frame.getContentPane().add(b1); JButton b2 = new JButton("Two"); frame.getContentPane().add(b2); JTextField t1 = new JTextField("Text here"); frame.getContentPane().add(t1); frame.pack(); frame.setVisible(true);

BorderLayout JFrame.setDefaultLookAndFeelDecorated(true); JFrame frame = new JFrame("Border"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JButton b1 = new JButton("At the top"); frame.getContentPane().add(b1,BorderLayout.PAGE_START ); JButton b2 = new JButton("Bottom"); frame.getContentPane().add(b2,BorderLayout.PAGE_END); JTextField t1 = new JTextField("Left"); frame.getContentPane().add(t1,BorderLayout.LINE_START); JTextField t2 = new JTextField("Right"); frame.getContentPane().add(t2,BorderLayout.LINE_END); JButton b3 = new JButton("Centre"); frame.getContentPane().add(b3,BorderLayout.CENTER ); frame.pack(); frame.setVisible(true);

Grid Layout JFrame.setDefaultLookAndFeelDecorated(true); JFrame frame = new JFrame("Grid"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.getContentPane().setLayout(new GridLayout(4,3,5,5)); for (int i=0; i<10; i++) frame.getContentPane().add(new JButton(""+i)); frame.pack(); frame.setVisible(true);

Swing has a lot of classes controls User I/O widgets eg JButton containers things that hold other things eg JFRame

Containers general purpose containers - panel scroll pane split pane tabbed pane tool bar top level containers - JFrame JApplet JDialog

JPanel ( in createAndShowGUI) JFrame.setDefaultLookAndFeelDecorated(true); JFrame frame = new JFrame("I am a JFrame"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBounds(20,30,300,100); frame.setLayout(null); //Create a panel JPanel myPanel = new JPanel(); myPanel.setBackground(new Color(255,3,25)); myPanel.setOpaque(true); //Make it the content pane. frame.setContentPane(myPanel); frame.setVisible(true);

Tooltip and border myPanel.setOpaque(true); myPanel.setToolTipText("I'm a JPanel"); myPanel.setBorder(BorderFactory.createLineBor der(Color.white)); frame.setContentPane(myPanel);..

JSplitPane setLayout(null); //Create a split pane JSplitPane myPane = new JSplitPane(); myPane.setOpaque(true); frame.setContentPane(myPane); frame.setVisible(true);

JSplitPane with JPanels //Create a split pane JSplitPane myPane = new JSplitPane(); myPane.setOpaque(true); myPane.setDividerLocation(150); // make two panels JPanel right = new JPanel(); right.setBackground(new Color(255,0,0)); JPanel left = new JPanel(); left.setBackground(new Color(0,255,0)); // set as left and right in split myPane.setRightComponent(right); myPane.setLeftComponent(left);

Exercise