Thread: Applet ClassFormatError and magic values

I am trying to turn a console application into an applet I have code that builds a GUI for a calculator that compiles and runs as expected:

import java.awt.GridBagLayout;
import java.awt.GridBagConstraints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
import java.lang.*;
 
public class CalculatorGUI extends JFrame
{
    JButton button;
    JTextField screen;
    //OperandListener opnLis = new OperandListener(this);
    //OperatorListener optLis = new OperatorListener(opnLis);
 
    CalculatorGUI()
    {
        setSize(150, 150);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setResizable(false);
        setVisible(true);
 
        setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
 
        screen = new JTextField("0", 15);
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.gridwidth = 4;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("7");
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("8");
        gbc.gridx = 0;
        gbc.gridy = 1;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("9");
        gbc.gridx = 0;
        gbc.gridy = 2;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("+");
        gbc.gridx = 0;
        gbc.gridy = 3;
        gbc.gridwidth = 1;
        //button.addActionListener(optLis);
        add(button);
 
        button = new JButton("4");
        gbc.gridx = 1;
        gbc.gridy = 0;
        gbc.gridwidth = 1;
        button.addActionListener(opnLis);
        add(button);
 
        //button = new JButton("5");
        gbc.gridx = 1;
        gbc.gridy = 1;
        gbc.gridwidth = 1;
        button.addActionListener(opnLis);
        add(button);
 
        //button = new JButton("6");
        gbc.gridx = 1;
        gbc.gridy = 2;
        gbc.gridwidth = 1;
        button.addActionListener(opnLis);
        add(button);
 
        //button = new JButton("-");
        gbc.gridx = 1;
        gbc.gridy = 3;
        gbc.gridwidth = 1;
        button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("1");
        gbc.gridx = 2;
        gbc.gridy = 0;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("2");
        gbc.gridx = 2;
        gbc.gridy = 1;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("3");
        gbc.gridx = 2;
        gbc.gridy = 2;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("*");
        gbc.gridx = 2;
        gbc.gridy = 3;
        gbc.gridwidth = 1;
        //button.addActionListener(optLis);
        add(button);
 
        button = new JButton(".");
        gbc.gridx = 3;
        gbc.gridy = 0;
        gbc.gridwidth = 1;
        button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("0");
        gbc.gridx = 3;
        gbc.gridy = 1;
        gbc.gridwidth = 4;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("=");
        gbc.gridx = 3;
        gbc.gridy = 2;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("/");
        gbc.gridx = 3;
        gbc.gridy = 3;
        gbc.gridwidth = 1;
        //button.addActionListener(optLis);
        add(button);
    }
}

The code for the applet is:

import java.awt.GridBagLayout;
import java.awt.GridBagConstraints;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JApplet;
import javax.swing.JTextField;
import java.lang.*;
 
public class CalculatorApplet extends JApplet
{
    JButton button;
    JTextField screen;
    //OperandListener opnLis = new OperandListener(this);
    //OperatorListener optLis = new OperatorListener(opnLis);
 
    CalculatorApplet()
    {
        setSize(150, 150);
        //setDefaultCloseOperation(EXIT_ON_CLOSE);
        //setResizable(false);
        setVisible(true);
 
        setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
 
        screen = new JTextField("0", 15);
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.gridwidth = 4;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("7");
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("8");
        gbc.gridx = 0;
        gbc.gridy = 1;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("9");
        gbc.gridx = 0;
        gbc.gridy = 2;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("+");
        gbc.gridx = 0;
        gbc.gridy = 3;
        gbc.gridwidth = 1;
        //button.addActionListener(optLis);
        add(button);
 
        button = new JButton("4");
        gbc.gridx = 1;
        gbc.gridy = 0;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("5");
        gbc.gridx = 1;
        gbc.gridy = 1;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("6");
        gbc.gridx = 1;
        gbc.gridy = 2;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("-");
        gbc.gridx = 1;
        gbc.gridy = 3;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("1");
        gbc.gridx = 2;
        gbc.gridy = 0;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("2");
        gbc.gridx = 2;
        gbc.gridy = 1;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("3");
        gbc.gridx = 2;
        gbc.gridy = 2;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("*");
        gbc.gridx = 2;
        gbc.gridy = 3;
        gbc.gridwidth = 1;
        //button.addActionListener(optLis);
        add(button);
 
        button = new JButton(".");
        gbc.gridx = 3;
        gbc.gridy = 0;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("0");
        gbc.gridx = 3;
        gbc.gridy = 1;
        gbc.gridwidth = 4;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("=");
        gbc.gridx = 3;
        gbc.gridy = 2;
        gbc.gridwidth = 1;
        //button.addActionListener(opnLis);
        add(button);
 
        button = new JButton("/");
        gbc.gridx = 3;
        gbc.gridy = 3;
        gbc.gridwidth = 1;
        //button.addActionListener(optLis);
        add(button);
    }
 
    public void init()
    {
        new CalculatorApplet();
    }
}

The appletviewer throws the following error:

java.lang.ClassFormatError: Incompatible magic value 1181314149 in class file Project
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClassCond(Unknown Source)
	at java.lang.ClassLoader.defineClass(Unknown Source)
	at java.security.SecureClassLoader.defineClass(Unknown Source)
	at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
	at sun.plugin2.applet.Plugin2ClassLoader.loadClass0(Unknown Source)
	at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
	at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
	at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
	at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)
Exception: java.lang.ClassFormatError: Incompatible magic value 1181314149 in class file Project

Due to personal technology woes, I am using the compilr.com online compiler and embedded appletviewer, so it may be a problem with how the specific compiler builds the class file. I don't have the option of using the JDK compiler, so I can't figure out I have a compiler-specific problem.

Are you sure that the class files are correct? The magic value should be CA FE BA BE, but yours is 46 69 6C 65, which translates into the ASCII "File", which leads me to believe something has gone awry.

If you could attach the Project.class and Project.java files, I'd be more than happy to take a look at them.