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1、Java语言程序设计授课教师：刘玉江1第四章 Applet及其应用1.Applet概述2.Applet类3.Applet程序与HTML文件4.Applet的应用2Applet概述nJava程序的两种基本形式nJava Application(应用程序)，可独立运行nJava Applet(小程序)，嵌入在浏览器中运行n超文本标记语言(HTML)nWWW浏览器nApplet小程序的运行方式n嵌入在/写入在HTML文件中n从WWW服务器下载到本地WWW浏览器n由WWW浏览器中的Java解释器来运行3一个Applet小程序的例子import java.applet.Applet;import jav
2、a.awt.Graphics;public class Exam4_1 extends Applet String str;public void init() str = “Here is an Applet”;public void paint(Graphics g) g.drawString(str, 100, 100);4HTML文件n实现过程nApplet小程序编写，编译，得到字节码文件njavac Exam4_1.javan嵌入到HTML文件中，保存为Exam4_1.htmlnnnnnn5HTML文件n浏览器打开Exam4_1.html文件6Applet的特点n通常作为Applet
3、类的子类，格式如下:public class 类名 extends Applet n嵌入在HTML文件中，利用WWW浏览器或Appletviewer来运行7Applet的工作原理Applet源程序字节码文件嵌入到HTML文件WWW浏览器打开 该HTML文件8第四章 Applet及其应用1.Applet概述2.Applet类3.Applet程序与HTML文件4.Applet的应用9Applet类的主要方法10Applet类的主要方法1.init()方法n完成初始化操作n在Applet程序第一次加载时调用，仅执行一次2.start()方法n启动Applet主线程运行n重启时也被调用(reload或
4、返回)3.paint()方法n将结果输出/绘制到界面上n被自动调用(启动后/窗口改变/repaint()调用)11Applet类的主要方法4.stop()方法n暂停Applet程序执行5.destroy()方法n终止Applet程序执行，释放所占用的资源12Applet类的主要方法import java.applet.Applet;import java.awt.*;public class Exam extends Applet public void init( ) /初始化Applet程序public void start( ) /启动Applet线程public void paint(
5、Graphics g) /绘制输出显示信息public void stop( ) /暂停线程public void destroy( ) /释放系统资源，结束线程13import java.applet.Applet；import java.awt.Graphics；public class L1 extends Applet StringBuffer bnew StringBuffer()； public void init()addWords(”初始化”)； public void start()addWords(”开始”)； public void stop()addWords(”停止”
6、)；public void destroy()addWords(”清除”)；void addWords(String s) System.out.println(s)； b.append(s)； repaint()； public void paint(Graphics g) g.drawstring(b.toString(),5,15)； 举例说明Applet程序的方法14l1.html:15第四章 Applet及其应用1.Applet概述2.Applet类3.Applet程序与HTML文件4.Applet的应用16HTML文件n超文本标记语言(HTML)n和nHtml文件开始和结束的标记n
7、和nWWW浏览器窗口标题内容的标记n和nHtml文件在浏览器窗口中显示内容的标记n和n嵌入到Html文件中Applet程序的标记17Applet程序的标记nnn参数n183.Applet标签属性：目的：将Applet程序嵌入web页中。语法格式如下： alternateHTML 19Applet小程序import java.applet.Applet;import java.awt.*;public class Exam4_3 extends Applet String str;int x, y, h;Font fnt;public void init() str = getParameter
8、(“string”);h = Integer.parseInt(getParameter(“size”);x = Integer.parseInt(getParameter(“x1”);y = Integer.parseInt(getParameter(“y1”);fnt = new Font(“TimesRoman”, Font.BOLD, h);public void paint(Graphics g) g.setColor(Color.red);g.setFont(fnt);g.drawString(str, x, y);20Applet小程序21第四章 Applet及其应用1.Appl
9、et概述2.Applet类3.Applet程序与HTML文件4.Applet的应用22绘制图形1.设置字体njava.awt.Font类n设置文本的字体(包括字型和字号)n构造方法npublic Font(String name, int style int size)2.设置颜色njava.awt.Color类n控制颜色，Color类已包含13个颜色常量n构造方法npublic Color(int r, int g, int b)npublic Color(float r1, float g1, float b1)23绘制图形3.绘制文本n绘制字符串npublic void drawStri
10、ng(String s, int x, int y)n绘制字符npublic void drawString(char c, int offset, int number int x, int y)n绘制字节npublic void drawString(byte b, int offset, int number int x, int y)24Applet小程序import java.applet.Applet;import java.awt.*;public class Exam4_4 extends Applet public void paint(Graphics g) Font fo
11、nt1, font2, font3;font1 = new Font(“Serif”, Font.BOLD, 20);font2 = new Font(“Monospaced”, Font.BOLD+Font.ITALIC, 24);font3 = new Font(“SansSerif”, Font.PLAIN, 16);g.setFont(font1);g.drawString(“Serif 20 point BOLD”, 30, 20);g.setFont(font2);g.drawString(“Monospaced 24 point BOLD + ITALIC”, 30, 80);g
12、.setFont(font3);g.drawString(“SansSerif 16 point PLAIN”, 30, 50);int size = font2.getSize();int style = font1.getStyle();String name = font2.getName();String str = name + “ “ + style + “ “ + size;g.drawString(str, 30, 110);25Applet小程序26Applet小程序import java.applet.Applet;import java.awt.*;public clas
13、s Exam4_6 extends Applet Font font1 = new Font(“TimesRoman”, Font.ITALIC, 25);Font font2 = new Font(“Braggadcoio”, Font.BOLD, 40);public void paint(Graphics g) String str = “I love Beijing!”;Color mycolor = new Color(192, 64, 200);g.setFont(font1);g.setColor(mycolor);g.drawString(str, 30, 40);Color
14、darker = mycolor.darker();g.setColor(darker);g.drawString(str, 50, 80);Color brighter = mycolor.brighter();g.setColor(brighter);g.drawString(str, 70, 120);g.setFont(font2);g.setColor(Color.red);g.drawString(str, 30, 170);g.setColor(Color.white);g.drawString(str, 32, 169);27Applet小程序28绘制图形4.绘制几何图形n画直
15、线nvoid drawLine(int x1, int y1, int x2, int y2)n画矩形nvoid drawRect(int x, int y, int width, int height)nvoid fillRect(int x, int y, int width, int height)nvoid clearRect(int x, int y, int width, int height)nvoid drawRoundRect(int x, int y, int width, int height, int arcWidth, int arcHeight)nvoid draw
16、3DRect(int x, int y, int width, int height, boolean b)nvoid fill3DRect(int x, int y, int width, int height, boolean b)29绘制图形4.绘制几何图形n画圆弧和椭圆nvoid drawArc(int x, int y, int width, int height, int startAngle, int arcAngle)nvoid fillArc(int x, int y, int width, int height, int startAngle, int arcAngle)n
17、void drawOval(int x, int y, int width, int height)nvoid fillOval(int x, int y, int width, int height)30Applet小程序import java.applet.Applet;import java.awt.*;public class Exam4_8 extends Applet public void paint(Graphics g) int x0 =10, y0=20, X=150, Y=80, L, c;int arc = 0, N=10;double xy=1.0*(X-Y)/N/2
18、;g.setColor(Color.red);g.fillRect(x0, y0, X, X);for(int i=0; i =N; i+) L=(int)(X-2*i*xy); arc=Y*i/N; c=i*240/N; g.setColor(new Color(c, c, c); g.drawRoundRect(int)(x0+i*xy), (int)(y0+i*xy), L, L, arc, arc);g.setColor(Color.blue);g.draw3DRect(200, y0, X, X, true);g.setColor(Color.green);g.fill3DRect(
19、400, y0, Y, Y, false);31Applet小程序32绘制图形4.绘制几何图形n画多边形npublic void drawPolygon(int xPoints, int yPoints, int Points)npublic void fillPolygon(int xPoints, int yPoints, int Points)npublic void drawPolygon(Polygon p)npublic void fillPolygon(Polygon p)nPolygon类构造方法nPolygon()nPolygon(int xPoints, int yPoin
20、ts, int numberOfPoints)33演示图像1.定义图像对象njava.awt.Image类n图像高度和宽度nint getHeight(ImageObserver observer)nint getWidth(ImageObserver observer)2.获取图像信息方法nImage getImage(URL url, String name)3.显示图像的操作ndrawImage(Image img, int x, int y, ImageObserver observer)ndrawImage(Image img, int x, int y, int width, in
21、t height, ImageObserver observer)34Applet小程序import java.applet.Applet;import java.awt.*;public class Exam4_13 extends Applet public void paint(Graphics g) Image pic;pic = getImage(getDocumentBase(), “edonkey.jpg”);int x0 = 10, y0 = 30;int w = pic.getWidth(this);int h = pic.getHeight(this);g.drawImag
22、e(pic, x0, y0, w/8, h/8, this);g.drawImage(pic, x0+150, y0, w/12, h/12, this);g.drawImage(pic, x0+150, y0+100, w/15, h/15, this);g.drawImage(pic, x0+250, y0+30, (int)(w*0.1), (int)(h*0.2), this);35Applet小程序36演示图像4.动画n创建Image类的对象数组ndrawImage()nThread.sleep()方法nrepaint()5.播放声音npublic void play(URL url)npublic AudioClip getAudio(URL url)nplay()方法/loop()方法/stop()方法37作业：1.简述Applet类的工作原理。2.P184 4538
