Problemas no Jframe

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.border.TitledBorder;


public class Exercicio1 extends JFrame implements ActionListener{
		JCheckBox chkN,chkC,chkD,chkT;
		JButton btnKrica;
	public Exercicio1(){
		chkN = new JCheckBox("natação");
		chkC = new JCheckBox("ciclismo");
		chkD = new JCheckBox("dança");
		chkT = new JCheckBox("todos");
		btnKrica = new JButton("krikaki");
		btnKrica.addActionListener(this);
		JPanel p = new JPanel(new GridLayout(4,1));
		TitledBorder titulo = BorderFactory.createTitledBorder("hobby");
		p.setBorder(titulo);
		p.add(chkN);
		p.add(chkC);
		p.add(chkD);
		p.add(chkT);
		add(p,"CENTER");
		add(btnKrica,"SOUTH");
		pack();
		setVisible(true);
	}
	public void actionPerformed(ActionEvent e){
		String resp = "";
		boolean nada = true;
		
		if (e.getSource() == chkT && !chkT.isSelected()){
			chkN.setSelected(false);
			chkC.setSelected(false);
			chkD.setSelected(false);
			
		}
		if (e.getSource() == chkT && chkT.isSelected()){
			chkN.setSelected(false);
			chkC.setSelected(false);
			chkD.setSelected(false);
		
		
	}
		if (e.getSource() == btnKrica && chkT.isSelected()){
			resp = chkN.getText() + " "+chkC.getText()+" "+chkD.getText();
			JOptionPane.showMessageDialog(this, resp);
		}
	}
	public static void main(String[] args) {
		new Exercicio1();
		
		
	}

}

Exception in thread “main” java.lang.IllegalArgumentException: cannot add to layout: unknown constraint: CENTER

at java.awt.BorderLayout.addLayoutComponent(Unknown Source)

at java.awt.BorderLayout.addLayoutComponent(Unknown Source)

at javax.swing.JRootPane$1.addLayoutComponent(Unknown Source)

at java.awt.Container.addImpl(Unknown Source)

at java.awt.Container.add(Unknown Source)

at javax.swing.JFrame.addImpl(Unknown Source)

at java.awt.Container.add(Unknown Source)

at Exercicio1.(Exercicio1.java:31)

at Exercicio1.main(Exercicio1.java:59)