Java Pyramid

import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JEditorPane;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;


public class a {

    public String building_1;
    public String building_2;
    public String building_3;
    public String building_4;
    public String building_5;
    public JEditorPane showPyr;

    private JFrame Pyramid;
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    a window = new a();
                    window.Pyramid.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
    public a() {
        initialize();
    }
    private void initialize() {
        Pyramid = new JFrame();
        Pyramid.setResizable(false);
        Pyramid.setTitle("Pyramid");
        Pyramid.setBounds(100, 100, 250, 200);
        Pyramid.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Pyramid.getContentPane().setLayout(null);

        building_1 = " ***** ";
        building_2 = "  *****  \n ****** ";
        building_3 = "   ***   \n  *****  \n ****** ";
        building_4 = "     *    \n   ***   \n  *****  \n ****** ";

        JButton btnNewButton = new JButton("Start");
        btnNewButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                start_build();
            }
        });
        btnNewButton.setBounds(62, 139, 122, 23);
        Pyramid.getContentPane().add(btnNewButton);

        showPyr = new JEditorPane();
        showPyr.setEditable(false);
        showPyr.setBounds(0, 0, 242, 128);
        Pyramid.getContentPane().add(showPyr);
    }

    public void start_build(){
        showPyr.setText("");
        try {
            Thread.sleep(1);
            showPyr.setText(building_1);
            Thread.sleep(1);
            showPyr.setText(building_2);
            Thread.sleep(1);
            showPyr.setText(building_3);
            Thread.sleep(1);
            showPyr.setText(building_4);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}