When I run the Codename One HelloWorld Java Program from the Codename One HelloWorld Tutorial, I get an error

When I run the Codename One HelloWorld Java Program from the Codename One HelloWorld Tutorial video, I get this error:
java: cannot find symbol
symbol: class Button
location: class com.acmecorp.appname.AppName

I think I'm missing an import for class Button. How do I add the import statement for class Button so that the compilation won't have this error?

Here is my source code:

package com.acmecorp.appname;
import static com.codename1.ui.CN.*;
import com.codename1.ui.Display;
import com.codename1.ui.Form;
import com.codename1.ui.Dialog;
import com.codename1.ui.Label;
import com.codename1.ui.plaf.UIManager;
import com.codename1.ui.util.Resources;
import com.codename1.io.Log;
import com.codename1.ui.Toolbar;
import java.io.IOException;
import com.codename1.ui.layouts.BoxLayout;
import com.codename1.io.NetworkEvent;
/**
* This file was generated by <a href="https://www.codenameone.com/">Codename One</a> for the purpose 
* of building native mobile applications using Java.
*/
public class AppName {
private Form current;
private Resources theme;
public void init(Object context) {
// use two network threads instead of one
updateNetworkThreadCount(2);
theme = UIManager.initFirstTheme("/theme");
// Enable Toolbar on all Forms by default
Toolbar.setGlobalToolbar(true);
// Pro only feature
Log.bindCrashProtection(true);
addNetworkErrorListener(err -> {
// prevent the event from propagating
err.consume();
if(err.getError() != null) {
Log.e(err.getError());
}
Log.sendLogAsync();
Dialog.show("Connection Error", "There was a networking error in the connection to " + err.getConnectionRequest().getUrl(), "OK", null);
});        
}
public void start() {
if(current != null){
current.show();
return;
}
Form hi = new Form("Hi World", BoxLayout.y());
hi.add(new Label("Hi World"));
Button b = new Button("Show Dialog");
hi.add(b);
b.addActionListener((e) -> Dialog.show("Dialog Title", "Hi", "OK", null));
hi.show();
}
public void stop() {
current = getCurrentForm();
if(current instanceof Dialog) {
((Dialog)current).dispose();
current = getCurrentForm();
}
}
public void destroy() {
}
}

I guess this com.codename1.ui.Button might works for u.