Why this Java error occurred?

Here's my 7-line code, supposedly making a dialog box saying "It worked!":
import javax.swing.*;
class MyFirstProgram {
public static void main(String[] arg) {
JOptionPane.showMessageDialogue;(nul… "It works!");
System.exit(0);
}
}
I get this error when trying to compile it using javac:
hello.java:4: error: cannot find symbol
JOptionpane.showMessageDialogue((null)…
(the arrow..) ^
I'm writing the code exactly how my textbook tells me, so why is this happening and how can I fix it?
