private void start(){
		reset();
		
		base=new JFrame(" Calculadora ");
		base.setSize(400,250);
		base.setLocation(450,250);
		base.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
		visor=new JTextField("0");
		visor.setHorizontalAlignment(JTextField.RIGHT);
		visor.setBackground(Color.white);
		visor.setFont(new Font("Lucida Sans Unicode",Font.BOLD,22));
		visor.setEditable(false);
		
		painel1=new JPanel();
		painel1.setLayout(new BorderLayout());
		
		painel2=new JPanel();
		painel2.setLayout(new GridLayout(5,4));
		
		painel1.add(visor, java.awt.BorderLayout.NORTH);
		painel1.add(painel2, java.awt.BorderLayout.CENTER);

		botoes=new JToggleButton[20];
		botoes[0]=new JToggleButton("0");  	    // pos 12
		
		botoes[1]=new JToggleButton("1");		// pos 8
		botoes[2]=new JToggleButton("2");		// pos 9
		botoes[3]=new JToggleButton("3"); 		// pos 10
		
		botoes[4]=new JToggleButton("4");		// pos 4
		botoes[5]=new JToggleButton("5"); 		// pos 5
		botoes[6]=new JToggleButton("6"); 		// pos 6
		
		botoes[7]=new JToggleButton("7"); 		// pos 0
		botoes[8]=new JToggleButton("8");		// pos 1
		botoes[9]=new JToggleButton("9"); 		// pos 2
		botoes[10]=new JToggleButton("/"); 		// pos 3
		
		botoes[11]=new JToggleButton("-");      // pos 11
		
		botoes[12]=new JToggleButton("*");		// pos 7
		
		botoes[13]=new JToggleButton(".");		// pos 13
		botoes[14]=new JToggleButton("=");		// pos 14
		botoes[15]=new JToggleButton("+");		// pos 15
		botoes[16]=new JToggleButton("+/-");	// pos 16
		botoes[17]=new JToggleButton("SQR");	// pos 17
		botoes[18]=new JToggleButton("SQRT");	// pos 18
		botoes[19]=new JToggleButton("RESET");	// pos 19

		for(int i=0;i<20;i++){
			botoes[i].setFont(new Font("Lucida Sans Unicode",Font.BOLD,16));
			botoes[i].addActionListener(new EventoListener());
		}
		
		for(int i=7;i<11;i++)	
			painel2.add(botoes[i]);
			
		for(int i=4;i<7;i++)	
			painel2.add(botoes[i]);
		
		painel2.add(botoes[12]);
		
		for(int i=1;i<4;i++)	
			painel2.add(botoes[i]);
			
		painel2.add(botoes[11]);
		painel2.add(botoes[0]);
		
		for(int i=13;i<20;i++)	
			painel2.add(botoes[i]);
		
		base.getContentPane().add(painel1);
		base.setVisible(true);
	}