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Java Applet A Java applet class that cannot run standalone. It must be called by a html page. To run a Java applet class, you may either use a Java enabled browser or appletviewer that inside the Java System Development Kit. A sample Java applet <html> <head> <title>hello</title> </head> <body> <applet code=test.class </applet> </body> </html> width=200 height=200> Java compiler (input *.java output *.class) test.java import java.applet.Applet; import java.awt.*; Each public class should have its own file. (public test class match test.java) public class test extends Applet { public void paint(Graphics g) { g.drawString("Hello, World!",10,100); } } CS303 Advanced Topics in Internet S ystems, Lecture1, Page 1/8 Output Hello, World! In the above example, a Java applet class activates by an applet tag in the html page. In the html page, the applet tag calls an external Java class “hello.class”. hello.class is the complied product of hello.java. Moreover, the name hello.java should match the public class hello. The first two lines are import statements that are the same as #include statement in C language. The public paint function is the basic display function in AWT(Abstract Window Toolkit). AWT is a graphic user interface library in JAVA. This is the same as MFC in Visual C++, OWL in Borland C++. Applet Life Cycle Init Start Stop / quit Stop restart Event loop, if the applet is valid. clean up Destroy CS303 Advanced Topics in Internet S ystems, Lecture1, Page 2/8 import java.applet.Applet; import java.awt.*; public class hello extends Applet { String output; public hello() { output="Constructor"; System.out.println("Constructor"); repaint(); } public void init() { output+=" Initialzation"; System.out.println("Initialzation"); repaint(); } public void start() { output+=" Start"; System.out.println("Start"); repaint(); } public void stop() { output+=" Stop"; System.out.println("Stop"); repaint(); } CS303 Advanced Topics in Internet S ystems, Lecture1, Page 3/8 public void destory() { output+=" Destory"; System.out.println("Destory"); repaint(); } public void paint(Graphics g) { g.drawString(output,10,100); } } Output D:\project\hello>appletviewer vj3b0.html Constructor Initialzation Start Stop Stop Start Start again Stop Quit D:\project\hello> constructor When a class is created, it calls the constructor. init To initialize the applet each time it is load or reloaded. start CS303 Advanced Topics in Internet S ystems, Lecture1, Page 4/8 To start the applet’s execution, such as when the applet is loaded or when the user revisits a page that contains the applet. stop To stop the applet’s execution, for example, when the user leaves the applet’s page or quits the browser. destory To perform a final cleanup in preparation for unloading. AWT Graphic Demo (test.java) import java.applet.Applet; import java.awt.*; public class test extends Applet { public void paint(Graphics g) { showStatus("AWT Graphic Demo"); // set status bar setBackground(Color.blue); setForeground(Color.cyan); // set background // set foreground color g.drawString("This is a string.",10,10); // output string g.drawLine(10,30,100,30); // draw line g.drawRect(10,40,90,80); // draw rectangle g.drawRoundRect(10,130,90,50,20,20);// draw round rectangle g.draw3DRect(10,190,90,50,true); // draw 3D rectangle g.drawOval(10,250,30,50); // draw oval int x[]={10,20,40,60}; int y[]={310,340,310,340}; g.drawPolygon(x,y,4); // draw polygon g.fillRect(10,350,60,50); // fill rectangle CS303 Advanced Topics in Internet S ystems, Lecture1, Page 5/8 g.fillRoundRect(120,10,60,50,20,20); // fill round rectangle g.fill3DRect(120,70,90,50,true); // fill 3D rectangle g.fillOval(120,130,30,50); // fill oval int x1[]={130,140,160,180}; int y1[]={210,240,210,240}; g.fillPolygon(x1,y1,4); // fill polygon } } CS303 Advanced Topics in Internet S ystems, Lecture1, Page 6/8 Display an image The function getImage() may read an external graphic file then create a graphic image. getDocumentBase() returns the current application path. drawImage() in the paint function can display the image to the Java virtual machine. The Java language supports either GIF image or JPEG image. import java.applet.Applet; import java.awt.*; public class test extends Applet { Image img; public void init() { img=getImage(getDocumentBase(),"12 apostle.jpg"); } public void paint(Graphics g) { g.drawImage(img,0,0,300,300,this); } } CS303 Advanced Topics in Internet S ystems, Lecture1, Page 7/8 Play a sound file The Java supports *.au sound file only. You may convert your sound file to au format by audiotool application. import java.applet.*; import java.awt.*; public class test extends Applet { AudioClip sound; public void init() { sound=getAudioClip(getDocumentBase(),"bark.au"); sound.play(); } } CS303 Advanced Topics in Internet S ystems, Lecture1, Page 8/8