option pane error in java code example

Example 1: dialog box in java swing

import javax.swing.JOptionPane;

public class Main {
  public static void main(String[] argv) throws Exception {

    JOptionPane.showMessageDialog(null, "I am happy.");

  }
}

Example 2: java joptionpane

JOptionPane.showMessageDialog(frame, "Eggs are not supposed to be green.");