Java SE (Java Platform, Standard Edition)

import  javax.swing.JOptionPane;

public class test1
{
	public static void main(String args[])
	{
		JOptionPane.showMessageDialog(null,"Hello world",JOptionPane.PLAIN_MESSAGE);
	}
}

By compiling the above code it is giving the following error:

test1.java:7: cannot find symbol
symbol : method showMessageDialog(<nulltype>,java.lang.String,int)
location: class javax.swing.JOptionPane
JOptionPane.showMessageDialog(null,"Hello world",JOptionPane.PLA
IN_MESSAGE);
^
1 error

Can anyone help me about this?

Thanks.