JDesktopPanecom Layout nulo;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class a extends JFrame implements ActionListener{

	private JButton b1;
	private JButton b2;
	private JMenuBar menubar;
	private JMenu menu;
    private JMenuItem menuitem;
    private JDesktopPane desktop;
    	
	public a(){
	
		this.getContentPane().setLayout(null);
		this.getContentPane().setBackground(Color.GREEN);		
		this.setSize(500, 500);
		this.setLocation(1, 1);
		this.setResizable(true);
		this.setTitle("a") ;
		
		menubar = new JMenuBar();
		setJMenuBar(menubar);
		
		desktop = new JDesktopPane();
		this.getContentPane().add(desktop);
		
		menu = new JMenu("Arquivo");
		menuitem = new JMenuItem("Calculadora");
		
		menubar.add(menu);
		menu.add(menuitem);
		menuitem.addActionListener(this);
			
		
		b1 = new JButton("BOTAO");
		b1.setBounds(new Rectangle(0,0,250,500));
		this.getContentPane().add(b1);
		
		b2 = new JButton("BOTAO");
		b2.setBounds(new Rectangle(250,0,250,500));		
		this.getContentPane().add(b2);
		
		
}		
		public void actionPerformed (ActionEvent e){
			if (e.getSource()==menuitem){
				Calculadora calc = new Calculadora();
				desktop.add(calc);
				calc.show();
				/* Calculadora é um internalframe que foi testado varias vezes em
				 *outros frames, sendo q sempre ficou visível*/
			}
		}
		public static void main(String[] args){
			new a().show();
		}
		
		
}

desktop = new JDesktopPane();
add(desktop);

desktop = new JDesktopPane();
this.getContentPane().add(desktop);
desktop.setBounds (new Rectangle(0,0,500,500));