Create a window with a JTextPane and a JMenuBar to modify aspects of text

I am trying to make a simple exercise work for me in which I want to create a window with a JTextPane and a JMenuBar to modify aspects of all the text within the JTextPane (not just the selected one) as size, bold or font. I want the changes you make to the text, for example, to make it bold, to accumulate to the following changes as I touch the items of the JMenuBar. For this I have created a class in which I pass through the parameters of the constructor the 3 variables of setFont. I have also created 3 other variables in the main class to save the parameters of the constructor and so the changes I make to the text format are accumulated. The problem I have at this point, I can not keep the changes in these variables.

package graficosyventanas;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ejercicio_practico__procesador_texto {


    public static void main(String[] args) {

        marq.setBounds(150,150,1000,450);
        marq.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        marq.add(lam);
        lam.setLayout(new BorderLayout());
        lam.add(mibarra, BorderLayout.NORTH);
        lam.add(texto, BorderLayout.CENTER);
        mibarra.add(fuente);
        mibarra.add(estilo);
        mibarra.add(tamanio);

        agrex fuente1 = new ejercicio_practico__procesador_texto().new agrex("Verdana", est, tam, fuente,"Verdana");
        agrex estilo1 = new ejercicio_practico__procesador_texto().new agrex(fu, Font.BOLD, tam, estilo,"Negrita");
        agrex estilo2 = new ejercicio_practico__procesador_texto().new agrex(fu, Font.PLAIN, tam, estilo,"Normal");
        agrex fuente2 = new ejercicio_practico__procesador_texto().new agrex("Calibri", est, tam, fuente,"Calibri");

        marq.setVisible(true);
    }

    private static JFrame marq = new JFrame();

    private static JMenuBar mibarra = new JMenuBar();
    private static JTextPane texto = new JTextPane();
    private static JPanel lam = new JPanel();
    private static JMenu fuente = new JMenu("Fuente");
    private static JMenu tamanio = new JMenu("Tamaño");
    private static JMenu estilo = new JMenu("Estilo");

    private static String fu="Arial";  //las 3 variables para que se me acumulen los cambios de formato del texto
    private static int est=Font.PLAIN;
    private static int tam=12;

    private static agrex tamanio1 = new ejercicio_practico__procesador_texto().new agrex(fu, est, 20, tamanio,"20");

    private class agrex {
            public agrex(String fuent, int estil, int taman, JMenu x,String titulo){

                JMenuItem item = new JMenuItem(titulo);
                x.add(item);
                item.addActionListener(new ActionListener(){

                        public void actionPerformed(ActionEvent e) {        //clase interna anónima

                        texto.setFont(new Font(fuent,estil,taman));
                        tam=taman;
                        est=estil;
                        fu=fuent;
                        System.out.print(fu + ", ");
                        System.out.print(est + ", ");
                        System.out.println(tam);
                    }
                });
            }
          }
        }