Problemas num programa simples

import java.applet.*;
import java.awt.*;

public class dialog extends Applet
{
	DialogFrame frame;
	Button button;

	public void init()
	{
		frame = new DialogFrame("DIALOG_FRAME");
		button = new Button("Abrir Janela");
		add(button);
	}

	public boolean action(Event evt, Object arg)
	{
		boolean visivel = frame.isShowing();
		if(visivel)
		{
			frame.hide();
			button.setLabel("Abrir Janela");
		}
		else
		{
			frame.show();
			button.setLabel("Fechar Janela");
		}
		return true;
	}
}

class DialogFrame extends Frame
{
	MenuBar menubar;
	Menu menu;
	MenuItem menuitem;
	Dialog dialog;
	TextField textfield;
	Button button;
	String	string;

	DialogFrame(String title)
	{
		super(title);

		menubar = new MenuBar();
		setMenuBar(menubar);
		menu = new Menu("Variáveis");
		menubar.add(menu);
		menuitem = new MenuItem("Dialog_Box");
		menu.add(menuitem);
		string = "	";
	}

	public void paint(Graphics g)
	{
		resize(300,250);
		g.drawString("O texto que você digitou:", 70, 100);
		g.drawString(string, 70, 120);
	}

	public boolean action(Event evt, Object arg)
	{
		if(evt.target instanceof MenuItem)
		{
			if(arg == "Dialog_Box")
			ShowDialogBox();
		}
		[b]else if(evt.target instanceof Button)
			if(arg == "Ok")
			{
				dialog.hide();
				repaint();
			}[/b]
		return true;
	}

protected void ShowDialogBox()
{
	dialog = new Dialog(this, "DIALOG_BOX", true);
	FlowLayout layout = new FlowLayout();
	dialog.setLayout(layout);
	dialog.resize(350, 200);

	button = new Button("Ok");
	dialog.add(button);
	textfield = new TextField(20);
	dialog.add(textfield);
	string = textfield.getText();

	dialog.show();
}
}