Java讲义范例Java讲义范例.doc

程序运行过程：javac 编译，java 运行 FirstProgram.java class Test{ public static void main(){ System.out.println(Hello,my first java program!); } } 编译：javac FirstProgram.java 错误：FirstProgram.java:1: class Test is public, should be declared in a file named Test.javajavac FirstProgram.java 运行：java FirstProgram 错误：Exception in thread main java.lang.NoSuchMethodError: main 原因：程序的入口函数声明必须为public static void main(String args[])。 修改：第二行改为public static void main(String args[]){ 编译：javac FirstProgram.java 运行：java FirstProgram 结果：Hello,my first java program! Another.java 修改FirstProgram.java的代码为： class FirstProgram{ public static void main(String args[]){ Another another=new Another(); another.say(); } } public class Another{ public void say(){ System.out.println(Another one.); } } 编译：javac FirstProgram.java 错误：FirstProgram.java:7: class Another is public, should be declared in a file named Another.java public class Another{ ^ 1 errorAnother.java（或删除public） 编译：javac Another.java 运行：java Another 错误：Exception in thread main java.lang.NoSuchMethodError: main 原因：java Another的含义为，程序从Another类的main方法开始运行，但程序的Another类中并没有main方法。 运行：java FirstProgram 结果：Another one. FirstAppliet.java FirstApplet.html public class FirstApplet{ public void paint(Graphics g) { g.setColor(Color.blue); g.drawString(Java是一门很优秀的语言,12,30); g.setColor(Color.red); g.drawString(我一定认真学习Java,22,56); } } applet code=FirstApplet.class height=100 width=300 /applet 编译：javac FirstApplet.java 错误：FirstApplet.java:2: cannot find symbol symbol : class Graphics location: class FirstApplet public void paint(Graphics g) { …… 原因：无法识别Graphics类，没有引入相关的类包。 修改：添加 import java.applet.*; import java.awt.*; 编译：javac FirstApplet.java 运行： appletviewer FirstApplet.html 错误：java.lang.ClassCastException: FirstApplet at sun.applet.AppletPanel.createApplet(AppletPanel.java:710) at sun.applet.AppletPanel.runLoader(AppletPanel.java:639)