Valor do Button em um JTextField

import javax.swing.JOptionPane;

public class calc extends javax.swing.JFrame {

    public calc() {
        initComponents();
    }

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

        jFrame1 = new javax.swing.JFrame();
        jFrame2 = new javax.swing.JFrame();
        jInternalFrame1 = new javax.swing.JInternalFrame();
        jSeparator1 = new javax.swing.JSeparator();
        BotaoNumero1 = new javax.swing.JButton();
        jMenuBar1 = new javax.swing.JMenuBar();
        jMenu1 = new javax.swing.JMenu();
        jMenuItem2 = new javax.swing.JMenuItem();
        jMenu2 = new javax.swing.JMenu();
        jMenuItem1 = new javax.swing.JMenuItem();
        jScrollPane1 = new javax.swing.JScrollPane();
        CampoNumero = new javax.swing.JTextPane();

        javax.swing.GroupLayout jFrame1Layout = new javax.swing.GroupLayout(jFrame1.getContentPane());
        jFrame1.getContentPane().setLayout(jFrame1Layout);
        jFrame1Layout.setHorizontalGroup(
            jFrame1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 400, Short.MAX_VALUE)
        );
        jFrame1Layout.setVerticalGroup(
            jFrame1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 300, Short.MAX_VALUE)
        );

        javax.swing.GroupLayout jFrame2Layout = new javax.swing.GroupLayout(jFrame2.getContentPane());
        jFrame2.getContentPane().setLayout(jFrame2Layout);
        jFrame2Layout.setHorizontalGroup(
            jFrame2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 400, Short.MAX_VALUE)
        );
        jFrame2Layout.setVerticalGroup(
            jFrame2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 300, Short.MAX_VALUE)
        );

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jInternalFrame1.setVisible(true);

        BotaoNumero1.setText("1");
        BotaoNumero1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                BotaoNumero1ActionPerformed(evt);
            }
        });

        jMenu1.setText("Arquivo");

        jMenuItem2.setText("Item");
        jMenu1.add(jMenuItem2);

        jMenuBar1.add(jMenu1);

        jMenu2.setText("Sobre");

        jMenuItem1.setText("Item");
        jMenu2.add(jMenuItem1);

        jMenuBar1.add(jMenu2);

        jScrollPane1.setViewportView(CampoNumero);

        javax.swing.GroupLayout jInternalFrame1Layout = new javax.swing.GroupLayout(jInternalFrame1.getContentPane());
        jInternalFrame1.getContentPane().setLayout(jInternalFrame1Layout);
        jInternalFrame1Layout.setHorizontalGroup(
            jInternalFrame1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jInternalFrame1Layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(jInternalFrame1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(jScrollPane1, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, 364, Short.MAX_VALUE)
                    .addComponent(jSeparator1, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, 364, Short.MAX_VALUE)
                    .addComponent(BotaoNumero1))
                .addContainerGap())
        );
        jInternalFrame1Layout.setVerticalGroup(
            jInternalFrame1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jInternalFrame1Layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 28, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGap(18, 18, 18)
                .addComponent(jSeparator1, javax.swing.GroupLayout.PREFERRED_SIZE, 10, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(BotaoNumero1)
                .addContainerGap(183, Short.MAX_VALUE))
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jInternalFrame1)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jInternalFrame1)
        );

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

private void BotaoNumero1ActionPerformed(java.awt.event.ActionEvent evt) {                                             
// TODO add your handling code here:
    BotaoNumero1.setText("1");
    CampoNumero.setText(BotaoNumero1.getText());
    System.out.print(CampoNumero.getText());

}                                            

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new calc().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify
    private javax.swing.JButton BotaoNumero1;
    private javax.swing.JTextPane CampoNumero;
    private javax.swing.JFrame jFrame1;
    private javax.swing.JFrame jFrame2;
    private javax.swing.JInternalFrame jInternalFrame1;
    private javax.swing.JMenu jMenu1;
    private javax.swing.JMenu jMenu2;
    private javax.swing.JMenuBar jMenuBar1;
    private javax.swing.JMenuItem jMenuItem1;
    private javax.swing.JMenuItem jMenuItem2;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JSeparator jSeparator1;
    // End of variables declaration

}