SIMPLE APPLET PROGRAM

Size: px

Start display at page:

Download "SIMPLE APPLET PROGRAM"

Arabella Horn
6 years ago
Views:

1 APPLETS Applets are small applications that are accessed on Internet Server, transported over Internet, automatically installed and run as a part of web- browser Applet Basics : - All applets are subclasses of class Applet. All java applets must import java.awt.*; and java.applet.*; Applets interact with the user through Abstract Window Toolkit(AWT). & not through console based I/O classes. AWT contains support for window based graphical interface. Java applets since run by Web- browser need AWT.

2 APPLET BASICS Applet Basics : - Execution of an applet does not begin from main( ). Output for applets is not handled by System.out.println( ), but there are various methods of AWT, such as drawstring( ). Once an applet is compiled, it is included in an HTML file using the APPLET tag. Applets are executed by Java- enabled Web browsers;when it encounters the APPLET tag; within an HTML file.

3 SIMPLE APPLET PROGRAM Simple Applet Program : - import java.awt.*; import java.applet.*; public class Ex extends Applet { public void paint(graphics g) { g.drawstring( Hello,40,50); } }

4 SIMPLE APPLET PROGRAM paint( ) method must be overridden by the applet.defined in AWT class. paint( ) must be called each time the applet wants to redisplay its o/p. It has one parameter of Graphics type. drawstring() is the method of Graphics class with foll syntax : void drawstring(string msg, int xpos, int ypos) xpos & ypos means x & y-coordinates in pixels respectively.

5 APPLET CLASS Applet Class : - Hierarchy of Applet class is as follows: Component Container Panel Applet

6 Methods Included in Applet class Method void destroy() String getappletinfo( ) URL getcodebase( ) URL getdocumentbase( ) String getparameter(string paramname) void init( ) Description Called to terminate an applet Returns a String that describes the Applet Returns the URL associated with the invoking applet. Returns the URL of the HTML file that invokes the applet. Returns the parameter associated with paramname. null is returned if parameter is not found. Called to initialize an applet.

7 APPLET ARCHITECTURE Applet Architecture: - All applets have an event driven architecture Applets wait for an event to occur AWT notifies the applet about the event generated by calling the event handler provided by the applet. Applet takes appropriate action & returns the control to AWT

8 APPLET SKELETON import java.awt.*; import java.applet.*; /*<applet code = Ex width=300 height = 500></applet>*/ public class Ex extends Applet { public void init( ) { //Used to initialize the applet } public void start( ) { // Used to begin/resume execution of applet } public void stop( ) {// suspend execution } public void destroy( ) { // To terminate an applet } public void paint(graphics g){ //Used to redraw output on applet } }

9 C:\jdk1.3\bin> javac Ex.java APPLETS C:\jdk1.3\bin> appletviewer Ex.java O/p Appletviewer :Ex Applet _

10 Syntax : void setbackground(int color) SIMPLE APPLET DISPLAY METHODS drawstring( ) :- Method of Graphics class. Used to draw text on the Applet window. Syntax : void drawstring(string msg, int xpos,int ypos) Eg : Graphics g; g.drawstring( Hello,10,20); setforeground( ) & setbackground() :- Method of Applet class. Used to set the Background color of the applet& Foreground color of the text.

11 REQUEST REPAINTING We can never create loop inside paint() i:e for scrolling text we cannot use paint( ) For that we make the use of repaint(). repaint( ) : Defined in AWT package. repaint() when invoked calls update() which in turn calls paint( ) repaint( ) -> update( ) -> paint() Syntax : It has 4 forms : void repaint( ): Entire window is repainted. void repaint(int left, int top, int width, int height) void repaint(long maxdelay) void repaint(long maxdelay, int left, int top, int width, int height)

12 HTML APPLET TAG Applet tag is used to start an applet both from an appletviewer and from an HTML document. The appletviewer will allow only one applet to be viewed one on window; whereas in web browsers we can run more than one applet on one single web page.

13 HTML APPLET TAG SYNTAX : <APPPLET [CODEBASE = codebaseurl] CODE = applet File [ALT = alternate text] [ NAME = appletinstancename] [ALIGN = alignment] [VSPACE = vertical space in pixels ] [HSPACE = horizontal space in pixels] WIDTH = pixels HEIGHT = pixels]

14 HTML APPLET TAG <PARAM NAME = AttributeName1 VALUE = AttributeValue1 > <PARAM NAME = AttributeName2 VALUE = AttributeValue2> </APPLET>

15 CODEBASE : Optional Attribute HTML APPLET TAG Specifies the base URL of the applet code.which is the directory that will be searched for the applet s executable class file. CODE : Required Attribute Gives the name of the file containing the applet code. ALT : Optional Attribute Used to specify a small text message if the web- browser understands APPLET tag but can t run it.

16 NAME Optional Attribute HTML APPLET TAG Used to specify name to applet instance. Helps us to communicate between applets by name. To obtain an Applet by name we have getname( ) defined in AppletContext interface. WIDTH & HEIGHT : Required Attribute Give size of an applet window. ALIGN : Optional Attribute Specifies alignment of applet window.

17 HTML APPLET TAG ALIGN : Constants specified are : LEFT, RIGHT,TOP, BOTTOM, MIDDLE, BASELINE, TEXTTOP, ABSMIDDLE, ABSBOTTOM. VSPACE & HSPACE : Optional Attribute VSPACE specifies the space in pixels above and below the applet. HSPACE specifies the space in pixels On right and left side of the applet.

18 PASSING PARAMETERS TO PARAM NAME & VALUE Optional Attribute APPLET allows to specify applet specific arguments in an HTML page. Applets access their attributes with getparameter( ). getparameter( ) returns the value of specified parameter in form of String object. Thus for numeric and boolean values we need to convert the string into their internal formats. SYNTAX : String getparameter(string paramname)

19 PASSING PARAMETERS TO import java.awt.*; APPLET import java.applet.*; public class HTMLAPPLET extends Applet { String msg; public void init() { msg = "hello"; } public void start() { String s = getparameter("font");

20 PASSING PARAMETERS TO APPLET if(s.equals("times New Roman")) { msg = s; } } public void paint(graphics g) { g.drawstring(msg, 50, 60 ); } }

21 PASSING PARAMETERS TO APPLET <HTML> <HEAD> </HEAD> <BODY BGCOLOR="000000"> <CENTER> <APPLET code = "HTMLAPPLET.class" width = "500" height = "300"

22 PASSING PARAMETERS TO align = RIGHT APPLET VSPACE = 300 HSPACE = 200 > <PARAM NAME = Font VALUE = "Times New Roman"> </APPLET> </CENTER> </BODY> </HTML>

23 WORKING WITH FONTS Fonts : - To select a new Font, you must construct a Font object that describes that font. One of these Constructor has foll general form : Font(String fontname, int fontstyle,int pointsize) fontname == > desired fontname. fontsyle three constants are included in this : Font.PLAIN, Font.BOLD, Font.ITALIC To combine styles together we write it in foll manner : Font.ITALIC Font.BOLD

24 WORKING WITH FONTS Fonts : - After constructing the object we should then make the use of setfont( ) void setfont(font obj)

25 WORKING WITH FONTS import java.awt.*; import java.applet.*; public class HTMLAPPLET extends Applet { String msg; Font f; public void init() { msg = "hello"; f = new Font( Dialog,Font.PLAIN,12); setfont(f); }

26 WORKING WITH FONTS public void paint(graphics g) { g.drawstring(msg,20,40); }

27 WORKING WITH GRAPHICS Graphics : - All graphics are drawn relative to a window. Graphics class consists of number of drawing functions. Drawing Lines : void drawline(int startx,int starty, int endx, int endy) drawline( ) displays a line in the current drawing color that begins at startx, starty and ends at endx, endy

28 WORKING WITH GRAPHICS Drawing Rectangles : void drawrect(int top,int left, int bottom, int right) void fillrect(int top,int left, int bottom, int right) void drawroundrect(int top,int left, int bottom, int right, int xdiam, int ydiam) void fillroundrect(int top,int left, int bottom, int right, int xdiam, int ydiam)

29 WORKING WITH GRAPHICS Drawing Ellipses and Circles : void drawoval(int top,int left, int width, int Height) void filloval(int top,int left, int width, int height) Drawing Arcs : void drawarc(int top,int left, int width, int Height,int startangle, int sweepangle) void fillarc(int top,int left, int width, int Height,int startangle, int sweepangle)

30 WORKING WITH GRAPHICS Drawing Polygons void drawpolygon(int x[],int y[], int numpoints) void fillpolygon(int x[],int y[], int numpoints)

Module 5 Applets About Applets Hierarchy of Applet Life Cycle of an Applet

Module 5 Applets About Applets Hierarchy of Applet Life Cycle of an Applet About Applets Module 5 Applets An applet is a little application. Prior to the World Wide Web, the built-in writing and drawing programs that came with Windows were sometimes called "applets." On the Web,