Java Compile Error: class Appletprac is public, sh

When I am compiling the java program I am getting this error: class Appletprac is public, should be declared in a file named Appletprac.java

Here is my java code:

import java.applet.*;
import java.awt.*;        // Graphics Class
import javax.swing.*;
import java.awt.event.*;
/*<applet code="Appletprac.class" width="500" height="500"> </applet>*/
public class Appletprac extends JApplet implements ActionListener
{
JButton OK;
JRadioButton Font_Style1,Font_Style2,Font_Style3;
ButtonGroup bg;
JCheckBox Font_Family_Name;
JTextField jt;
int i;
         String s="";
public void init()
{
    OK=new JButton("OK");       
    Font_Family_Name=new JCheckBox("Serif");
    Font_Style1=new JRadioButton("Plain");
    Font_Style2=new JRadioButton("Bold");   
    Font_Style3=new JRadioButton("BoldItalic");
    bg=new ButtonGroup();
    jt=new JTextField(20);
    this.setLayout(new FlowLayout());
    bg.add(Font_Style1);
    bg.add(Font_Style2);
    bg.add(Font_Style3);    
                      this.add(jt);
    this.add(OK);
    this.add(Font_Family_Name);
    this.add(Font_Style1);
    this.add(Font_Style2);
    this.add(Font_Style3); 
    OK.addActionListener(this);
    Font_Style1.addActionListener(this);    
    Font_Style2.addActionListener(this);
    Font_Style3.addActionListener(this);
}
public void start()
{}
public void stop()
{}  
public void paint(Graphics g)
{
    g.clearRect(50,50,500,300);
    g.draw3DRect(50,50,500,300,false);
    g.setFont(new Font(s,i,30));
    g.setColor(Color.BLUE);
    g.drawString(jt.getText(),100,100);

}
public void actionPerformed(ActionEvent e)
{
    if(e.getSource()==Font_Style1)
        i=Font.PLAIN;
    if(e.getSource()==Font_Style2)
                  i=Font.BOLD;
    if(e.getSource()==Font_Style3)
    {
                  i=Font.ITALIC;
                  int j=Font.BOLD;
                  i=i+j;
    }       
    if(e.getSource()==Font_Family_Name || e.getSource()==OK)
    {
        if(Font_Family_Name.isSelected())
            s="Serif";
        else
                      s="Tall paul";
    }       
    repaint();
}
}

回答1:

Java allow one public class per file, and the public class name should be the same with the file name. For you , you should make the filename Appletprac.java

You can see this link Why are filenames in Java the same as the class name?

Write a html file like this:

test.html

<html>
<applet 
   code = Appletprac.class
   width = 200
   height = 100>
</applet>
</html>

Put the compiled .class file in the same folder, and input appletviewer test.html in the cmd.

回答2:

If your outer class has a public modifier it should be in the file with the same class name and .java extention. This is a simple java convention to structure classes and packages in the filesystem.