Which statements about the following program are correct

public class Bear $\{$

$$private Bear pandaBear;

$$private void roar$($Bear b$)\{$

$$System$.$out.println$("$Roar$!")$;

$$pandaBear $=$ b;

$\}$

$$public static void main$($String$[]$ args$)\{$

$$ Bear brownBear $=$ new Bear$()$;

$$ Bear polarBear $=$ new Bear$()$;

$$ brownBear.roar$($polarBear$)$;

$$ polarBear $=$ null;

$$ brownBear $=$ null;

$$ System.gc$()$; $\}\}$