Java Swing Datum

package delftstack;

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.LayoutManager;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.text.DateFormat;
import java.text.NumberFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.swing.BorderFactory;
import javax.swing.JFormattedTextField;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Show_Date implements PropertyChangeListener {
  public static void main(String[] args) {
    Show_Date DateShow = new Show_Date();
    createWindow(DateShow);
  }

  private static void createWindow(Show_Date DateShow) {
    JFrame J_Frame = new JFrame("Show Date");
    J_Frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    createUI(J_Frame, DateShow);
    J_Frame.setSize(300, 200);
    J_Frame.setLocationRelativeTo(null);
    J_Frame.setVisible(true);
  }

  private static void createUI(final JFrame J_Frame, Show_Date DateShow) {
    JPanel J_Panel = new JPanel();
    LayoutManager Layout_Manager = new GridLayout(6, 2);
    J_Panel.setLayout(Layout_Manager);
    J_Panel.setSize(200, 200);
    J_Panel.setBorder(BorderFactory.createTitledBorder("Date Format"));

    DateFormat Date_Format = new SimpleDateFormat("dd MMM YYYY");
    JFormattedTextField Today_Date = new JFormattedTextField(Date_Format);
    Today_Date.setName("Today");
    Today_Date.setColumns(10);
    Today_Date.setEditable(false);
    JLabel Today_Label = new JLabel("Date:");
    Today_Label.setLabelFor(Today_Date);
    Today_Date.setValue(new Date());

    J_Panel.add(Today_Label);
    J_Panel.add(Today_Date);
    JPanel Main_Panel = new JPanel();
    Main_Panel.add(J_Panel);

    J_Frame.getContentPane().add(Main_Panel, BorderLayout.CENTER);
  }

  @Override
  public void propertyChange(PropertyChangeEvent evt) {
    // TODO Auto-generated method stub
  }
}

package delftstack;

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

class DatePick {
  int DATE_MONTH = java.util.Calendar.getInstance().get(java.util.Calendar.MONTH);
  int DATE_YEAR = java.util.Calendar.getInstance().get(java.util.Calendar.YEAR);
  ;
  JLabel J_Label = new JLabel("", JLabel.CENTER);
  String DATE_DAY = "";
  JDialog J_Dialog;
  JButton[] J_Button = new JButton[49];

  public DatePick(JFrame J_Frame_Parent) {
    J_Dialog = new JDialog();
    J_Dialog.setModal(true);
    String[] Header = {
        "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
    JPanel J_Panel1 = new JPanel(new GridLayout(7, 7));
    J_Panel1.setPreferredSize(new Dimension(700, 120));

    for (int i = 0; i < J_Button.length; i++) {
      final int selection = i;
      J_Button[i] = new JButton();
      J_Button[i].setFocusPainted(false);
      J_Button[i].setBackground(Color.white);
      if (i > 6)
        J_Button[i].addActionListener(new ActionListener() {
          public void actionPerformed(ActionEvent ae) {
            DATE_DAY = J_Button[selection].getActionCommand();
            J_Dialog.dispose();
          }
        });
      if (i < 7) {
        J_Button[i].setText(Header[i]);
        J_Button[i].setForeground(Color.red);
      }
      J_Panel1.add(J_Button[i]);
    }
    JPanel J_Panel2 = new JPanel(new GridLayout(1, 3));
    JButton Previous_Button = new JButton("<< Previous");
    Previous_Button.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ae) {
        DATE_MONTH--;
        Display_Date();
      }
    });
    J_Panel2.add(Previous_Button);
    J_Panel2.add(J_Label);
    JButton Next_Button = new JButton("Next >>");
    Next_Button.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ae) {
        DATE_MONTH++;
        Display_Date();
      }
    });
    J_Panel2.add(Next_Button);
    J_Dialog.add(J_Panel1, BorderLayout.CENTER);
    J_Dialog.add(J_Panel2, BorderLayout.SOUTH);
    J_Dialog.pack();
    J_Dialog.setLocationRelativeTo(J_Frame_Parent);
    Display_Date();
    J_Dialog.setVisible(true);
  }

  public void Display_Date() {
    for (int i = 7; i < J_Button.length; i++) J_Button[i].setText("");
    java.text.SimpleDateFormat Simple_Date_Format = new java.text.SimpleDateFormat("MMMM yyyy");
    java.util.Calendar Calendar = java.util.Calendar.getInstance();
    Calendar.set(DATE_YEAR, DATE_MONTH, 1);
    int Day_Of_Week = Calendar.get(java.util.Calendar.DAY_OF_WEEK);
    int Days_In_Month = Calendar.getActualMaximum(java.util.Calendar.DAY_OF_MONTH);
    for (int i = 6 + Day_Of_Week, Day = 1; Day <= Days_In_Month; i++, Day++)
      J_Button[i].setText("" + Day);
    J_Label.setText(Simple_Date_Format.format(Calendar.getTime()));
    J_Dialog.setTitle("Date Picker");
  }

  public String Set_Picked_Date() {
    if (DATE_DAY.equals(""))
      return DATE_DAY;
    java.text.SimpleDateFormat Simple_Date_Format = new java.text.SimpleDateFormat("dd-MM-yyyy");
    java.util.Calendar Calendar = java.util.Calendar.getInstance();
    Calendar.set(DATE_YEAR, DATE_MONTH, Integer.parseInt(DATE_DAY));
    return Simple_Date_Format.format(Calendar.getTime());
  }
}

public class Date_Picker {
  public static void main(String[] args) {
    JLabel J_Label = new JLabel("Date Selected:");
    final JTextField J_Text_Field = new JTextField(20);
    JButton J_Button = new JButton("Choose the Date");
    JPanel J_Panel = new JPanel();
    J_Panel.add(J_Label);
    J_Panel.add(J_Text_Field);
    J_Panel.add(J_Button);
    final JFrame J_Frame = new JFrame();
    J_Frame.getContentPane().add(J_Panel);
    J_Frame.pack();
    J_Frame.setVisible(true);
    J_Button.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent ae) {
        J_Text_Field.setText(new DatePick(J_Frame).Set_Picked_Date());
      }
    });
  }
}