In java programming, Class Test

$\{$

int a$,$ b;

Test $($int i$,$ int j$)$

$\{$

a $=$ i;

b $=$ j;

$\}$

$/*$ Passed an object. Now, ob$.$a and ob$.$b in object used in the call will be changed. $*/$

void change$($Test ob$)$

$\{$

ob$.$a $=$ ob$.$a $+$ ob$.$b;

ob$.$b $=-$ob$.$b;

$\}$

$\}$

class PassObRef

$\{$

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

$\{$

Test ob $=$ new Test$(15,20)$;

System.out.println$("$ob$.$a and ob$.$b before call: $"+$ ob$.$a $+""$ ob$.$b$)$;

ob$.$change$($ob$)$;

System.out.println$("$ob$.$a and ob$.$b after call: $"+$ ob$.$a $+""+$ ob$.$b$)$;

$\}$

$\}$ A$.$ Explain how objects, a and b$,$ are passed to the method.

B$.$ Why primitive type cannot be used in the objects of this program?

C$.$ Explain how the call or changes of objects, a and b$,$ impact the output of the program.