Adicionar jpanel a um jpanel que esta numa jframe

mainPanel.add(new adduser());

public class adduser extends javax.swing.JPanel {

    /** Creates new form adduser */
    public adduser() {
        initComponents();
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {

        jLabel1 = new javax.swing.JLabel();

        org.jdesktop.application.ResourceMap resourceMap = org.jdesktop.application.Application.getInstance(pombalingua.PombalinguaApp.class).getContext().getResourceMap(adduser.class);
        setBackground(resourceMap.getColor("Form.background")); // NOI18N
        setName("Form"); // NOI18N

        jLabel1.setText(resourceMap.getString("jLabel1.text")); // NOI18N
        jLabel1.setName("jLabel1"); // NOI18N

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
        this.setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(39, 39, 39)
                .addComponent(jLabel1)
                .addContainerGap(337, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(23, 23, 23)
                .addComponent(jLabel1)
                .addContainerGap(262, Short.MAX_VALUE))
        );
    }// </editor-fold>


    // Variables declaration - do not modify
    private javax.swing.JLabel jLabel1;
    // End of variables declaration

}