使用 netbeans 中另一个 jFrame 的按钮关闭 jFrame？

我在 netbeans 中创建了两个 jFrame。第一个被命名为MainFrame另一个是ExternalFrame，每个都有一个按钮。单击按钮MainFrame将设置ExternalFrame可见与MainFrame仍然在屏幕上。我想处置MainFrame使用里面的按钮ExternalFrame。现在我很难弄清楚我该怎么做。我尝试把MainFrame.dispose(); and new MainFrame.setVisible(false);在 - 的里面ActionPerformed按钮，但两者都不起作用。

这是netbeans生成的代码MainFrame :

public class MainFrame extends javax.swing.JFrame {

public MainFrame() {
    initComponents();
}

@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {

    btn_OpenExternal = new javax.swing.JButton();
    jLabel1 = new javax.swing.JLabel();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setCursor(new java.awt.Cursor(java.awt.Cursor.DEFAULT_CURSOR));

    btn_OpenExternal.setText("Open External");
    btn_OpenExternal.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            btn_OpenExternalActionPerformed(evt);
        }
    });

    jLabel1.setText("MAIN FRAME");

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap(153, Short.MAX_VALUE)
            .addComponent(btn_OpenExternal)
            .addGap(146, 146, 146))
        .addGroup(layout.createSequentialGroup()
            .addGap(172, 172, 172)
            .addComponent(jLabel1)
            .addContainerGap())
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(81, 81, 81)
            .addComponent(jLabel1)
            .addGap(34, 34, 34)
            .addComponent(btn_OpenExternal)
            .addContainerGap(148, Short.MAX_VALUE))
    );

    pack();
}// </editor-fold>

private void btn_OpenExternalActionPerformed(java.awt.event.ActionEvent evt) {
    new ExternalFrame().setVisible(true);
}

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {
    /*
     * Set the Nimbus look and feel
     */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /*
     * If Nimbus (introduced in Java SE 6) is not available, stay with the
     * default look and feel. For details see
     * http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /*
     * Create and display the form
     */
    java.awt.EventQueue.invokeLater(new Runnable() {

        public void run() {
            new MainFrame().setVisible(true);
        }
    });
}
// Variables declaration - do not modify
private javax.swing.JButton btn_OpenExternal;
private javax.swing.JLabel jLabel1;
// End of variables declaration

}

这是代码ExternalFrame:

public class ExternalFrame extends javax.swing.JFrame {


public ExternalFrame() {
    initComponents();
}

@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    jLabel1 = new javax.swing.JLabel();
    btn_CloseMain = new javax.swing.JButton();
    jLabel2 = new javax.swing.JLabel();

    jLabel1.setText("jLabel1");

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    btn_CloseMain.setText("Close Main");
    btn_CloseMain.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            btn_CloseMainActionPerformed(evt);
        }
    });

    jLabel2.setText("EXTERNAL FRAME");

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
            .addContainerGap(167, Short.MAX_VALUE)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(jLabel2)
                .addComponent(btn_CloseMain))
            .addGap(146, 146, 146))
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(97, 97, 97)
            .addComponent(jLabel2)
            .addGap(18, 18, 18)
            .addComponent(btn_CloseMain)
            .addContainerGap(148, Short.MAX_VALUE))
    );

    java.awt.Dimension screenSize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
    setBounds((screenSize.width-416)/2, (screenSize.height-339)/2, 416, 339);
}// </editor-fold>                        

private void btn_CloseMainActionPerformed(java.awt.event.ActionEvent evt) {                                              
    MainFrame.setVisible(false); //this is has an error in my netbeans project
}                                             


/**
 * @param args the command line arguments
 */
public static void main(String args[]) {
    /*
     * Set the Nimbus look and feel
     */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /*
     * If Nimbus (introduced in Java SE 6) is not available, stay with the
     * default look and feel. For details see
     * http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(ExternalFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(ExternalFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(ExternalFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(ExternalFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /*
     * Create and display the form
     */
    java.awt.EventQueue.invokeLater(new Runnable() {

        public void run() {
            new ExternalFrame().setVisible(true);
        }
    });
}
// Variables declaration - do not modify                     
private javax.swing.JButton btn_CloseMain;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
// End of variables declaration                   

}