Code erro

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Container;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.ScrollPane;
import javax.swing.*;

public class Calc extends JFrame{
	private JTable t;
	private JScrollPane sp;
	private JTextField result;
    static final String rotulo[] = {"7", "8", "9", "4", "5", "6", "1", "2", "3", "0", "+", ","};
    private JButton btn[];
	public Calc(){
		super.getContentPane().setLayout(null);
	    JPanel keys = new JPanel(new GridLayout(4,3));
	    add(keys, new BorderLayout().CENTER);
	    btn[rotulo.length] = new JButton();
	    for (int i=1; i<rotulo.length; i++) {
	    	btn[i].setText(""+rotulo[i]);
	    	keys.add(btn[i]);
		}
	    result = new JTextField();
	    add(result, BorderLayout.NORTH);
	    keys.add(new JLabel("aqui nao tem pra niguem"));
	    keys.setBounds(10, 10, 50, 50);
	}
	    public static void main(String[] args) {
		Calc app = new Calc();
		app.setSize(300, 400);
		app.setLocation(300, 200);
		app.setVisible(true);
		app.setTitle("Calculadora 2 CPD");
		app.setDefaultCloseOperation(EXIT_ON_CLOSE);
	}
}

private JButton[] btn = new JButton[40];