when you want to find the number of days since 1/1/2001 import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.util.Date; import javax.swing.*; public class DaysSince { public static void main(String[] args) { JFrame frame = new JFrame("Days Since 1/1/2001"); JButton btn = new JButton("Find Number of Days Since 1/1/2001"); btn.setBounds(150,100,200, 40); btn.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent e){ Date startDate = new Date(2001,1,1); Date endDate = new Date(); long startTime = startDate.getTime(); long endTime = endDate.getTime(); long diffTime = endTime - startTime; long diffDays = diffTime / (1000 * 60 * 60 * 24); JOptionPane.showMessageDialog(frame, "Number of Days Since 1/1/2001: " + diffDays); } }); frame.add(btn); frame.setSize(500,500); frame.setLayout(null); frame.setVisible(true); } }