Thread: JOptionPane in Swing

I tried compiling this code but got an error in line 14. I don't understand what my problem is.
Here is the error that I encountered:
JOptionPane.java:14: error: cannot find symbol
JOptionPane.showMessageDialog(frame,"Content");
^
symbol: method showMessageDialog(JFrame,String)
location: class JOptionPane
1 error

Can anyone help me?

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

class JOptionPane
{

JFrame frame;

public void CreateFrame()
{
frame = new JFrame("Testing");
frame.setLayout(null);
frame.setBounds(0,0,500,400);
JOptionPane.showMessageDialog(frame,"Content");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOS E);

frame.setVisible(true);

}

public static void main(String args[])
{
JOptionPane obj = new JOptionPane();
obj.CreateFrame();
}

}