Why can't it find getPackageManager?

I have tried to open the Gmail app via this:

import android.content.Intent;


public class GmailApp {
    public static void OpenGmail() {

        Intent intent = getPackageManager().getLaunchIntentForPackage("com.google.android.gm");
        if(intent != null){
            startActivity(intent);
        }

    }
}

It says it can't find it. But how?

I've read this article right here Can't find getPackageManager() method in android

But I don't understand it.

Can anyone give me an example code that will work?