Here is the code block corrected:

//Insert missing code here.
import java.awt.*;
import java.awt.event.*;

public class JEMail extends JFrame implements ActionListener
{
    //Insert missing code here.
    private JTextField toField = new JTextField(24);
    private JLabel subjectLabel = new JLabel("Subject:");
    private JTextField subjectField = new JTextField(24);
    //Insert missing code here.
    private JButton sendButton = new JButton("Send");
    private JTextArea message = new JTextArea(4, 22);

    public JEMail()
    {
        super("WebBuy Company E-Mail");
        setSize(370, 270);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Container pane = getContentPane();
        FlowLayout flow = new FlowLayout(FlowLayout.RIGHT);
        pane.setLayout(flow);
    //Insert missing code here.
        panel1.add(toLabel);
    //Insert missing code here.
        pane.add(panel1);
        JPanel panel2 = new JPanel();
        panel2.add(subjectLabel);
        panel2.add(subjectField);
    //Insert missing code here.
        JPanel panel3 = new JPanel();
        panel3.add(messageLabel);
        message.setLineWrap(true);
        message.setWrapStyleWord(true);
        JScrollPane scroll = new JScrollPane(message,
           JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
           JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        panel3.add(scroll);
    //Insert missing code here.
        JPanel panel4 = new JPanel();
        panel4.add(sendButton);
        pane.add(panel4);
        sendButton.addActionListener(this);
    //Insert missing code here.
    }

    public static void main(String[] arguments)
    {
        JEMail email = new JEMail();
    //Insert missing code here.
    }
    public void actionPerformed(ActionEvent event)
    {
      Object source = event.getSource();
      if (source == sendButton)
        message.append("\nMail has been sent!");
    }
}