import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class Framecito extends JFrame implements ActionListener{

	private JPanel contentPane;

	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					Framecito frame = new Framecito();
					frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the frame.
	 */
	public Framecito() {
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(100, 100, 450, 300);
		contentPane = new JPanel();
		contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
		setContentPane(contentPane);
		contentPane.setLayout(null);
		Panelcito p=new Panelcito();
		Container conteiner=getContentPane();
		
		JButton btnClick = new JButton("Click");
		btnClick.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent arg0) {
				conteiner.removeAll();
				p.setVisible(true);
				conteiner.add(p);
				revalidate();
				repaint();
			}
		});
		btnClick.setBounds(149, 121, 89, 23);
		contentPane.add(btnClick);
	}

	@Override
	public void actionPerformed(ActionEvent arg0) {
		// TODO Auto-generated method stub
		
	}
}
 

  import javax.swing.JPanel;
import java.awt.Color;
import javax.swing.JLabel;
import java.awt.Font;

public class Panelcito extends JPanel {

	/**
	 * Create the panel.
	 */
	public Panelcito() {
		setBackground(Color.GREEN);
		setLayout(null);
		
		JLabel labell = new JLabel("ESTÁS DENTRO DEL PANEL");
		labell.setFont(new Font("Tahoma", Font.PLAIN, 15));
		labell.setBounds(101, 131, 254, 14);
		add(labell);

	}
}