$(2)$ Given:

public class X

Eprivate int $a$;

public int $b$;$.$

public static int $c$;

$3$

Given:

Class Y has main$(...$

Valid or invalid:

$x$@$b_j=$ new $)$;

$-b_j*a=20$;

$0j*b={30}^{\text{'}},$

$(3)$ main$(...)($Valid or invalid$)$

boolean $flg=$ objl $$ obj$2$;

$(4)$ From #$2$:

main $(...)$

$x*b_j=$ new $x()$;

Obj$*c=10$;

$x*c=20$;

Valid or invalid