下面是我的程序:
import java.io.*;
public class FileApp {
    public static void main (String args[]) 
    {
        byte buffer[]=new byte[2500];
        try
        {
            FileInputStream fileIn=new FileInputStream("newbook1.txt");
            int bytes=fileIn.read(buffer,0,2500);
            try
            {
                String str=new String(buffer,0,bytes,"Default");
                System.out.println(str);
            }
            catch(UnsupportedEncodingException e)
            {
                System.out.println("The encoding"Default"was not found:"+e);
            }
            fileIn.close();
        }
        catch(Exception e)
        {
            String err=e.toString();
            System.out.println("error:"+err);
        }
    }
}

用浏览器打开后总会提示:
java.lang.ClassCastException: FileApp
at sun.applet.AppletPanel.createApplet(AppletPanel.java:548)
at sun.plugin.AppletViewer.createApplet(AppletViewer.java:1621)
at sun.applet.AppletPanel.runLoader(AppletPanel.java:477)
at sun.applet.AppletPanel.run(AppletPanel.java:290)
at java.lang.Thread.run(Thread.java:536)

你这是简单java程序，故你只需要在IDE中run或dos下 java运行就可以了
浏览器是运行applet的
你这个不是applet
所以不行

import java.io.*;
import java.awt.*;
import java.applet.*;
public class FileApp extends Applet {
public void init() {
 byte buffer[]=new byte[2500];
        try
        {
            FileInputStream fileIn=new FileInputStream("newbook1.txt");
            int bytes=fileIn.read(buffer,0,2500);
            try
            {
                String str=new String(buffer,0,bytes,"Default");
                System.out.println(str);
            }
            catch(UnsupportedEncodingException e)
            {
                System.out.println("The encoding"Default"was not found:"+e);
            }
            fileIn.close();
        }
        catch(Exception e)
        {
            String err=e.toString();
            System.out.println("error:"+err);
        }
    
}}