1 / 35

Applet Example

Applet Example. Applets and applications. An applet is a Java program that runs on a web page Applets can be run within any modern browser To run modern Java applets, old browsers need an up-to-date Java plugin appletviewer is a program that can run

emmanuel-ramos
Télécharger la présentation

Applet Example

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Applet Example

  2. Applets and applications • An applet is a Java program that runs on a web page • Applets can be run within any modern browser • To run modern Java applets, old browsers need an up-to-date Java plugin • appletviewer is a program that can run • An application is a Java program that runs all by itself

  3. Applet • An applet is a program that comes from server into a client and gets executed at client side and displays the result. • An applet represents byte code embedded in a html page. (applet = bytecode + html) and run with the help of Java enabled browsers such as Internet Explorer. • An applet is a Java program that runs in a browser. Unlike Java applications applets do not have a main () method. To create applet we can use java.applet.Applet .

  4. Applet

  5. Packages and classes • Java supplies a huge library of pre-written “code,” ready for you to use in your programs • Code is organized into classes • Classes are grouped into packages • One way to use this code is to import it • You can import a single class, or all the classes in a package

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

  7. 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

  8. The java.awt package • “awt” stands for “Abstract Window Toolkit” • The java.awt package includes classes for: • Drawing lines and shapes • Drawing letters • Setting colors • Choosing fonts • If it’s drawn on the screen, then java.awt is probably involved!

  9. Importing the java.awt package • Since you may want to use many classes from the java.awt package, simply import them all: import java.awt.*; • The asterisk, or star (*), means “all classes” • The import directives can go in any order, but must be the first lines in your program

  10. The applet so far import java.applet.Applet;import java.awt.*;

  11. Your applet class public class Drawing extends Applet { … } • Drawing is the name of your class • Class names should always be capitalized • extends Applet says that our Drawing is a kind of Applet, but with added capabilities • Java’s Applet just makes an empty window • We are going to draw in that window • The only way to make an applet is to extend Applet

  12. The applet so far import java.applet.Applet;import java.awt.*; public class Drawing extends Applet { …we still need to put some code in here... }

  13. The paint method • Our applet is going to have a method to paint some colored rectangles on the screen • This method must be named paint • paint needs to be told where on the screen it can draw • This will be the only parameter it needs • paint doesn’t return any result

  14. The paint method, part 2 • public void paint(Graphics g) { … } • public says that anyone can use this method • void says that it does not return a result • A Graphics (short for “Graphics context”) is an object that holds information about a painting • It remembers what color you are using • It remembers what font you are using • You can “paint” on it (but it doesn’t remember what you have painted)

  15. The applet so far import java.applet.Applet;import java.awt.*; public class Drawing extends Applet { public void paint(Graphics g) {…we still need to put some code in here…}}

  16. Colors • The java.awtpackage defines a class named Color • There are 13 predefined colors—here are their fully-qualified names: • For compatibility with older programs (before the naming conventions were established), Java also allows color names in lowercase: Color.black, Color.darkGray, etc. Color.BLACK Color.PINK Color.GREENColor.DARK_GRAY Color.RED Color.CYANColor.GRAY Color.ORANGE Color.BLUEColor.LIGHT_GRAY Color.YELLOWColor.WHITE Color.MAGENTA

  17. New colors • Every color is a mix of red, green, and blue • You can make your own colors:new Color(red,green,blue) • Amounts range from 0 to 255 • Black is (0, 0, 0), white is (255, 255, 255) • We are mixing lights, not pigments • Yellow is red + green, or (255, 255, 0)

  18. Setting a color • To use a color, we tell our Graphicsgwhat color we want: g.setColor(Color.RED); • g will remember this color and use it for everything until we tell it some different color

  19. The paint method so far public void paint(Graphics g) { g.setColor(Color.BLUE);…draw a rectangle,write any string… g.setColor(Color.RED);…draw another rectangle write any string…}}

  20. Pixels • A pixel is a picture (pix) element • one pixel is one dot on your screen • there are typically 72 to 90 pixels per inch • java.awt measures everything in pixels

  21. (0, 0) (50, 0) (50, 20) (0, 20) (w-1, h-1) Java’s coordinate system • Java uses an (x, y) coordinate system • (0, 0) is the top left corner • (50, 0) is 50 pixels to the right of (0, 0) • (0, 20) is 20 pixels down from (0, 0) • (w - 1, h - 1) is just inside the bottom right corner, where w is the width of the window and h is its height

  22. Drawing rectangles • There are two ways to draw rectangles: • g.drawRect(left,top,width,height); • g.fillRect(left,top,width,height);

  23. The complete applet import java.applet.Applet;import java.awt.*; public class Drawing extends Applet { public void paint(Graphics g) { g.setColor(Color.BLUE); g.fillRect(20, 20, 50, 30); g.setColor(Color.RED); g.fillRect(50, 30, 50, 30); }}

  24. Some more java.awt methods • g.drawLine(x1 ,y1,x2 ,y2 ); • g.drawOval( left,top,width,height ); • g.fillOval( left,top,width,height); • g.drawRoundRect( left,top,width,height ); • g.fillRoundRect( left,top ,width,height); • g.drawArc( left,top,width,height,startAngle,arcAngle); • g.drawString(string,x,y);

  25. The HTML page • You can only run an applet in an HTML page • The HTML looks something like this: • <html> <body> <h1>DrawingApplet Applet</h1> <applet code="DrawingApplet.class" width="250" height="200"> </applet> </body></html> • BlueJ will create this HTML for you

  26. Programme-2 • import java.applet.*; import java.awt.*;publicclass HelloWorld extendsApplet {public void init() {       resize(150,25);       }//initpublic void paint(Graphics g) {       g.setFont(newFont("Helvetica", Font.PLAIN, 8));       g.drawString("Hello world!", 50, 25);       }//paint   }//HelloWorld Compiling and Executing Program: javac HelloWorld.java appletviewer test.HelloWorld.html

  27. Programme-1

  28. Programme-1 import java.applet.*; import java.awt.*; public class DrawingLines extends Applet { int width, height; public void init() { width = getSize().width; height = getSize().height; setBackground( Color.black ); } public void paint( Graphics g ) { g.setColor( Color.green ); for ( int i = 0; i < 10; ++i ) { g.drawLine( width, height, i * width / 10, 0 ); } }}

  29. Basic Methods(1/2) • Methods for Milestones • init() – initialize the applet • start() – start the applet’s execution • stop() – stop the applet’s execution • destroy() – perform a final cleanup

  30. Basic Methods(2/2) • Typical Structure import java.applet.Applet; import java.awt.Graphics; public class Simple extends Applet { ... public void init() { ... } public void start() { ... } public void stop() { ... } public void destroy() { ... } public void paint(Graphics g) { ... } } <APPLET CODE=... CODEBASE=... WIDTH=... HEIGHT=...> ... </APPLET> <HTML Code> <Applet Code>

  31. import java.applet.Applet; import java.awt.Graphics; public class HelloWorld extends Applet { public void paint(Graphics g) { g.drawString("Hello", 50,20); } } <APPLET CODE="HelloWorld.class“ WIDTH=200 HEIGHT=140> </APPLET> Example • Source Code • Result HelloWorld.java HelloWorld.htm

  32. Programme- • publicclass SetGraphicsColorExample extends Applet{ • publicvoid paint(Graphics g) { •                 /* •                  * Graphic objects like lines and rectangles uses current •                  * foreground color. •                  * •                  * To change the current graphic color use •                  * void setColor(Color c) method of Graphics Class. •                  */ •                 //this will create light blue color •                 Color customColor = new Color(10,10,255); •                 g.setColor(customColor); •                 g.drawLine(10,10,30,30); •                 g.setColor(Color.red); •                 g.fillRect(40,40,40,40); •                 g.setColor(Color.green); •                 g.fillRect(80,80,40,40); •                 g.draw3DRect(81,81,40,40,true); •         } • }

  33. Program Program 1: Write an applet program with a message and display the message in paint () method. /* <applet code="MyApplet.class" width = 600 height= 450> </applet> */

  34. Program

More Related