Why does the compiler create repeated .class files?

I have noticed that when the java compiler compiles some class that has some swing / awt component, it creates another or even several classes of the same name, with a $ followed by a numbering.

I made a simple code to check if it was a netbeans thing or if it was really the compiler and compiling the code below:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Tela {

    public Tela(){

        final JFrame frame = new JFrame("Tela 1");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JLabel label = new JLabel("teste");
        JButton button = new JButton("botao");
        button.addActionListener(new ActionListener(){

            public void actionPerformed(ActionEvent e){

            new DialogTela(frame, true);
            }

        });
        frame.setPreferredSize(new Dimension(175, 100));
        JPanel p = new JPanel(new FlowLayout());
        p.add(label);
        p.add(button);
        frame.getContentPane().add(p);

        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {

        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Tela();
            }
        });
    }

    class DialogTela{

        public DialogTela(Frame f, boolean modal){

        JDialog dialog = new JDialog(f,modal);

            dialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);

            JLabel label = new JLabel("teste");
            dialog.setPreferredSize(new Dimension(175, 100));
            JPanel p = new JPanel(new FlowLayout());
            p.add(label);
            dialog.getContentPane().add(p);

            dialog.pack();
            dialog.setVisible(true);
        }
    }   
}

Result after compile:

I'mnotsurewhythecompilercreatedtheTela$DialogTela.classandtheTela$1.class,inadditiontotheTela$2.classitself.

Forthesakeofconscience,IcreatedanotherclasscalledTela.class,whereIonlymakeacalltoaTeste(whichalsobelongstotheswingpackage):

importjavax.swing.JOptionPane;publicclassTeste{publicstaticvoidmain(String[]args){JOptionPane.showMessageDialog(null,"teste", "Teste", JOptionPane.INFORMATION_MESSAGE);
    }
}

and only JOptionPane was generated.

What would be those repeated classes that the compiler created from the same class? Is there any particularity of the swing API?