面向?qū)ο蠹夹g(shù)Java

1、 面向?qū)ο蠹夹g(shù)JavaObject-Oriental Technology Java 曾文權(quán)老師Email： 第9章 Java小應(yīng)用程序Applet 1第9章 Java小應(yīng)用程序Applet學(xué)習(xí)目標(biāo)(Course Objectives)了解小應(yīng)用程序的原理掌握小應(yīng)用程序的開發(fā)步驟 能用Java語言編寫小應(yīng)用程序 2第9章 Java小應(yīng)用程序Applet9.1 Applet入門9.2 Applet的開發(fā)步驟9.3 Applet的常用方法9.4 Applet的多媒體(Multimedia)應(yīng)用9.5 Applet間的通信 小結(jié)39.1 Applet Introduction引入：（1）C/B應(yīng)用模

2、式中，如何使Browser界面更為生動，即在Browser環(huán)境中實現(xiàn)圖像表示、聲音播放等多媒體功能？（2）具有對Browser客戶的交互事件處理、多線程運行、網(wǎng)絡(luò)訪問等靈活的Web功能。（3）安全、跨平臺的網(wǎng)絡(luò)應(yīng)用程序。?49.1 Applet IntroductionSolution：Java Applet?59.1 Applet Definition An applet is a program written in the JavaTM programming language that can be included in an HTML page, much in the same

3、way an image is included. When you use a Java technology-enabled browser to view a page that contains an applet, the applets code is transferred to your system and executed by the browsers Java Virtual Machine (JVM). 69.1 Applet SecutiryappletBrowserSERVER本地程序fileSERVERlocalconnectionconnectionApple

4、t被下載的與applet無關(guān)的本地方法Applet的沙箱模型7 Applications vs. Applets(1) Similarities They both are Java programs. (2) Differences An applet is a small program that is intended not to be run on its own, but rather to be embedded inside another application.8 Applications vs. AppletsPrivileges(1) Applets are not a

5、llowed to read from, or write to, the of the computer viewing the applets. (2) Applets are not allowed to run any programs on the browsers computer.(3) Applets are not allowed to establish connections between the users computer and another computer except with the server where the applets are stored

6、. 99.2 Applet的開發(fā)步驟編輯Applet的Java源文件( Edit Source Applet) import java.awt.*;import java.applet.*;public class JavaWorld extends Appletpublic void paint(Graphics g)g.drawString(Java World!,15,25);SourceFile: JavaWorld.java109.2 Applet程序開發(fā)步驟Compiling Programs:On command linejavac JavaWorld.javaByteCodeF

7、ile: JavaWorld.class11Creating an HTML with Applet: java World! ApppletHtmlFile: JavaWorld.html12Viewing Java Applets: 139.2 Applet程序開發(fā)步驟Applet Viewer Utility :appletviewer JavaWorld.htmlExample:appletviewer JavaWorld.htmlRun Applet Viewer149.2 Applet程序開發(fā)步驟運行結(jié)果159.2 Applet程序開發(fā)步驟_歸納(1) 編譯Appletjavac

8、JavaWorld.java(2) 創(chuàng)建HTML文件（JavaWorld.html)(3) 瀏覽JavaWorld.html Appletviewer JavaWorld.html 瀏覽器（Browser) java World! Appplet169.3 How to write Applet_Class、Method(1) Applet類是所有Applet應(yīng)用的基類。所有小應(yīng)用程序都要繼承java.applet.Applet類。該類由Sun公司事先定義好了.每個小應(yīng)用都有一個public類型的主程序類 import java.applet.*; public class MyApplet

9、extends Applet (2) Applet的主要方法public Applet()/構(gòu)造方法 public boolean isActive() /是否處于活動狀態(tài)public URL getDoucmentBase()/Applet運行目錄URL地址179.3 How to write Applet_Class、Methodpublic URL getCodeBase()/得到代碼的URL地址public void showStatus(String msg)/顯示狀態(tài)public getImage(URL url)/裝入圖象public void play(URL url)/播放音

10、頻剪輯public void destroy()/撤銷Applet，釋放資源189.3 How to write Applet_Class、Methodinit()方法對加載的applet進(jìn)行初始化start()方法在初始化后，自動調(diào)用start()方法離開網(wǎng)頁后返回，系統(tǒng)再執(zhí)行一遍start()stop()方法用戶離開網(wǎng)頁時調(diào)用destroy()方法關(guān)閉Applet，釋放資源191. Browser loads URL2. Browser loads HTML documentApplet class3. Browser loads applet classesLocation:Loadin

11、g.4. Browser run applet209.3 Write Html Embeded with AppletApplet和HTML(1) CODE標(biāo)記聲明Applet應(yīng)用的class文件名CODE=“TestApplet.class”(2) CODEBASE標(biāo)記指定Applet代碼的URL地址CODEBASE=“”(3) ALT標(biāo)志指定替代文本信息，如果找不到代碼，則顯示它ALT=“Java Not Support” 219.3 Write Html Embeded with Applet(4) ALIGN標(biāo)記Applet窗口在HTML文檔窗口中的位置，ALIGN的值可以是MIDDL

12、E、TOP和BOTTOM(5) VSPACE、HSPACE標(biāo)記指定Applet窗口周圍的空白(6) NAME標(biāo)記指定加載的Applet名字，以便其它Applet引用229.4 Applet的應(yīng)用_Multimedia利用Applet顯示圖像功能：支持兩種主要的圖像格式：GIF、JPEG。方法： Applet類提供了一個重要的方法： （1）獲得一個用于顯示在屏幕上的Image對象的引用： public Image getImage(URL url,String name)； （2）顯示圖像： public boolean drawImage(Image img,int x,int y, Imag

13、eObserver observer)； 注： 由于Applet類已經(jīng)實現(xiàn)了ImageObserver接口，因此它可以作為加載圖像時的圖像觀察器，即將this作為最后一個參數(shù)傳遞給drawImage()便可將Applet對象傳遞過去。 239.4 Applet的應(yīng)用_Multimedia例：利用Applet顯示圖像import java.awt.*;import java.applet.*;public class ShowImage extends AppletImage picture;public void init() picture=getImage(getCodeBase(),Im

14、age.gif);public void paint(Graphics g) g.drawImage(picture,0,0,this); 249.4 Applet的應(yīng)用_MultimediaDisplaying Images :259.4 Applet的應(yīng)用_MultimediaPlay Sound:功能：可以播放.au、.aiff、.wav、.midi、.rfm格式的音頻。方法：（1）獲得一個用于播放的音頻對象（AudioClip類型對象）: getAudioClip(Url url,String name);（2）處理聲音文件： play() 播放聲音文件 name; loop() 循環(huán)

15、播放name; stop() 停止播放name。269.4 Applet的應(yīng)用_MultimediaExample: Play Sound.import java.awt.*;import java.applet.*;public class Sound extends Applet public void paint(Graphics g) AudioClip audioClip=getAudioClip(getCodeBase(),Sample.AU); /也可以是WAV聲音文件 g.drawString(Sound Demo!,10,20); audioClip.loop(); /循環(huán)播

16、放 279.4 Applet的應(yīng)用_Multimedia如何利用Applet播放“鈴”聲(ringin.wav)?import java.awt.*;import java.applet.*;public class Sound extends Applet public void paint(Graphics g) AudioClip audioClip=getAudioClip(getCodeBase(),“ringin.wav); /也可以是WAV聲音文件 g.drawString(Sound Demo!,10,20); audioClip.loop(); /循環(huán)播放 289.5 App

17、let間的通信Applet之間的通信 同一HTML頁中的多個Applet利用其名字來區(qū)分彼此,并能相互通信。一個Applet可通過下面的方法得到其它Applet的引用: AppletContext ac=this.getAppletContext Applet applet=ac.getApplet(“Applet1”)其中Applet在HTML文件中用如下方式命名：299.5 Applet間的通信Applet之間通信示例30HTML Test PageApplet通信示例的html文件319.5 Applet間的通信Applet之間通信示例關(guān)鍵代碼Applet1:Applet2: Apple

18、tContext ac=this.getAppletContext(); Applet appletControl=ac.getApplet(Applet1); TextField textField=(TextField)appletControl.getComponent(3); textField.setText(textField1.getText();AppletContext ac=this.getAppletContext();Applet appletColor=ac.getApplet(Applet2);appletColor.setBackground(Color.red)32利用瀏覽器瀏覽Applet（1）前述主要使用AppletViewer瀏覽Applet。（2）若使用瀏覽器瀏覽Applet須安裝