private void btnReporteUsuarioActionPerformed(java.awt.event.ActionEvent evt) {
    // TODO add your handling code here:
    List lista = new ArrayList();
    for(int i=0; i<tblListCom.getRowCount(); i++){
        ListaUser user= new ListaUser(tblListCom.getValueAt(i, 9).toString(),tblListCom.getValueAt(i,4 ).toString(),tblListCom.getValueAt(i, 3).toString(),tblListCom.getValueAt(i, 2).toString(),tblListCom.getValueAt(i, 8).toString());
        lista.add(user);
        }

 try {
     JasperReport reporte = (JasperReport) JRLoader.loadObject("reporteuser.jasper");
      Map parametro = new HashMap();
        parametro.put("hostname",txtHost_com.getText());
        JasperPrint jprint = JasperFillManager.fillReport(reporte, parametro,new JRBeanCollectionDataSource(lista));
        JasperViewer.viewReport(jprint);
 } catch (JRException ex) {
     Logger.getLogger(ListCompu.class.getName()).log(Level.SEVERE, null, ex);
 }

}

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Ventanas.ListCompu.btnReporteUsuarioActionPerformed(ListCompu.java:935)
at Ventanas.ListCompu.access$1400(ListCompu.java:47)
at Ventanas.ListCompu$15.actionPerformed(ListCompu.java:444)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6533)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6298)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

ListaUser user= new ListaUser(tblListCom.getValueAt(i, 9).toString(),tblListCom.getValueAt(i,4 ).toString(),tblListCom.getValueAt(i, 3).toString(),tblListCom.getValueAt(i, 2).toString(),tblListCom.getValueAt(i, 8).toString());

public class ListaUser {
private String Nomina;
private String Equipo;
private String Marca;
private String Modelo;
private String SN;
private String Comentarios;

public ListaUser(String Nomina, String Equipo, String Marca, String Modelo, String SN, String Comentarios) {
    this.Nomina = Nomina;
    this.Equipo = Equipo;
    this.Marca = Marca;
    this.Modelo = Modelo;
    this.SN = SN;
    this.Comentarios = Comentarios;
}

public ListaUser(String toString, String toString0, String toString1, String toString2, String toString3) {
    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
}




public String getNomina() {
    return Nomina;
}

public void setNomina(String Nomina) {
    this.Nomina = Nomina;
}

public String getEquipo() {
    return Equipo;
}

public void setEquipo(String Equipo) {
    this.Equipo = Equipo;
}

public String getMarca() {
    return Marca;
}

public void setMarca(String Marca) {
    this.Marca = Marca;
}

public String getModelo() {
    return Modelo;
}

public void setModelo(String Modelo) {
    this.Modelo = Modelo;
}

public String getSN() {
    return SN;
}

public void setSN(String SN) {
    this.SN = SN;
}

public String getComentarios() {
    return Comentarios;
}

public void setComentarios(String Comentarios) {
    this.Comentarios = Comentarios;
}