Fechar JFrane

import javax.swing.SwingUtilities;   
import java.awt.BorderLayout;   
import javax.swing.JPanel;   
import javax.swing.JFrame;   
import javax.swing.JButton;   
import java.awt.Rectangle;   
  
public class Principal extends JFrame {   
  
    private static final long serialVersionUID = 1L;   
  
    private JPanel jContentPane = null;   
  
    private JButton jButtonCadastrar = null;   
  
    private JButton getJButtonCadastrar() {   
        if (jButtonCadastrar == null) {   
            jButtonCadastrar = new JButton();   
            jButtonCadastrar.setBounds(new Rectangle(51, 43, 142, 33));   
            jButtonCadastrar.setText("Cadastrar");   
            jButtonCadastrar.addActionListener(new java.awt.event.ActionListener() {   
                public void actionPerformed(java.awt.event.ActionEvent e) {   
                    System.out.println("actionPerformed()");   
                    Cadastrar cad = new Cadastrar();   
                    cad.show();   
                }   
            });   
        }   
        return jButtonCadastrar;   
    }   
  
    public static void main(String[] args) {   
        // TODO Auto-generated method stub   
        SwingUtilities.invokeLater(new Runnable() {   
            public void run() {   
                Principal thisClass = new Principal();   
                thisClass.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);   
                thisClass.setVisible(true);   
            }   
        });   
    }   
  
    public Principal() {   
        super();   
        initialize();   
    }   
  
    private void initialize() {   
        this.setSize(300, 200);   
        this.setContentPane(getJContentPane());   
        this.setTitle("JFrame");   
    }   
  
    private JPanel getJContentPane() {   
        if (jContentPane == null) {   
            jContentPane = new JPanel();   
            jContentPane.setLayout(null);   
            jContentPane.add(getJButtonCadastrar(), null);   
        }   
        return jContentPane;   
    }   
  
}

Form Secundario 


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import java.awt.BorderLayout;   
import javax.swing.JPanel;   
import javax.swing.JFrame;   
import javax.swing.JButton;   
import java.awt.Rectangle;   
  
public class Cadastrar extends JFrame {   
  
    private static final long serialVersionUID = 1L;   
  
    private JPanel jContentPane = null;   
  
    private JButton jButtonCadastrar = null;   
  
    public Cadastrar() {   
        super();   
        initialize();   
    }   
  
    private void initialize() {   
        this.setSize(300, 200);   
        this.setContentPane(getJContentPane());   
        this.setTitle("JFrame");   
    }   
  
    private JPanel getJContentPane() {   
        if (jContentPane == null) {   
            jContentPane = new JPanel();   
            jContentPane.setLayout(null);   
            jContentPane.add(getJButtonCadastrar(), null);   
        }   
        return jContentPane;   
    }   
  
    private JButton getJButtonCadastrar() {   
        if (jButtonCadastrar == null) {   
            jButtonCadastrar = new JButton();   
            jButtonCadastrar.setBounds(new Rectangle(33, 45, 176, 21));   
            jButtonCadastrar.setText("Fechar");   
            jButtonCadastrar.addActionListener(new java.awt.event.ActionListener() {   
                public void actionPerformed(java.awt.event.ActionEvent e) {   
                    System.out.println("actionPerformed()");   
                    Cadastrar cad = new Cadastrar();   
                    cad.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);   
                }   
            });   
        }   
        return jButtonCadastrar;   
    }   
  
}