java applet. introductions applet is java program that can be embedded into html pages java applets...
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Java Applet
Introductions
Applet is java program that can be embedded into HTML pagesJava 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 classThis class is in the java.applet packageThe Applet class contains code that works with a browser to create a display windowCapitalization 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 keywordjava.applet is the name of the packageA dot ( . ) separates the package from the classApplet is the name of the classThere 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 appletstart(): 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
[<] APPLET [CODEBASE = codebaseURL] CODE = appletFile [ALT = alternateText] [NAME = appletInstanceName] WIDTH = pixels HEIGHT = pixels [ALIGN = alignment] [VSPACE = pixels] [HSPACE = pixels] > [< PARAM NAME = appletParameter1 VALUE = value >] [< PARAM NAME = appletParameter2 VALUE = value >] . . [alternateHTML] [</]APPLET[>]
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
<HTML><HEAD></HEAD><BODY><APPLET ALIGN="CENTER" CODE="FirstApplet.class" WIDTH="800" HEIGHT="500"></APPLET></BODY></HTML>
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 parameterdrawString(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 colorg.fillColor(Color.color_name);Graphics.fillRect() :to fill the color inside the rectangle by specified colorg.fillRect(int X_coordinate, int Y_coordinate, int Wdth, int height)
Passing Parameter in Java Applet
The param tag(<parma name="" value=""></param>) 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 usedMediaTracker is a utility class that tracks the status of a number of media objectsimg - 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
IntroductionsSwing 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().getImage("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 Areaimport 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);TextFieldJTextField 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 itemsThere is a choice of these which work in different waysInitially 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);
BorderLayoutJFrame.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 thingseg 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.createLineBorder(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 paneJSplitPane myPane = new JSplitPane();myPane.setOpaque(true);myPane.setDividerLocation(150);// make two panelsJPanel 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 splitmyPane.setRightComponent(right); myPane.setLeftComponent(left);
Exercise
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