Which of the following would cause a syntax error?

Question $1$Answer

a$.$

A sub class reference variable referencing an object of the sub class type

b$.$

A sub class reference variable referencing an object of the type of the sub class's super class

c$.$

A super class reference variable referencing an object of the super class type

d$.$

A super class reference variable referencing an object of the type of one of its sub classes

e$.$

If you think none of the above will cause a syntax error, select this option

Question $2$

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Which is NOT a correct explanation of the code given below.

Question $2$Answer

a$.$

Person objRef $=$ new Lecturer$()$;

objRef.name $=$ "Goo";

is an example of Upcasting

b$.$

Lecturer lec $=($Lecturer$)$objRef;

lec.age $=21$;

is an example of Downcasting

c$.$

objRef.display$()$;

lec.display$()$;

outputs:

Lecturer

Lecturer

d$.$

System.out.println$($lec$.$name $+"/"+$ lec.age$)$;

outputs:

Goo$/21$

e$.$

The code will not compile.

Question $3$

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Which of the following is not true about a set of methods that are usefully polymorphic?

This question only considers inheritance$-$based polymorphism i$.$e$.$ it does not consider Interfaces.

Question $3$Answer

a$.$

They must have identical signatures and therefore belong to separate classes

b$.$

Their classes share a common ancestor class from which they are ultimately inherited

c$.$

Each should produce a specialised effect appropriate to their class and therefore different to each other

d$.$

To be invoked polymorphically, an object of their class's type must be referenced by a variable of an ancestor's type common to all of them

e$.$

If you think all of the above are true, select this option

Question $4$

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Which of the following is false with respect to downcasting.

Question $4$Answer

a$.$

It can be done without declaring a new variable

b$.$

It's necessary when you want to invoke a method available in the object's class but not in its reference variable's class

c$.$

The downcast must always be to the object's class

d$.$

You can only downcast between classes and$/$or interfaces connected in a class$/$Interface hierarchy

e$.$

Select this option if you think none of the above are false

Question $5$

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Which of the following are required for method overriding?

$($sub$/$super means the methods are in two classes that are in an inheritance relationship$)$

Question $5$Answer

a$.$

Same name, same signature, same class

b$.$

Same name, different signature, same class

c$.$

Same name, same signature, sub$/$super class

d$.$

Same name, different signature, sub$/$super class

e$.$

Select this option if you think none of the above are required.

Question $6$

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Assume that Student is a subclass of Person, and FIT$1051$Student is a subclass of Student.

Which of the following is not a valid reference, given

Student s $=$ new Student $("$Ash$","12345")$;

Question $6$Answer

a$.$

Student student $=$ s;

b$.$

Object o $=$ s;

c$.$

FIT$1051$Student student $=$ s;

d$.$

Person p $=$ s;

Question $7$

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Which of the following best describes polymorphism in Java?

Question $7$Answer

a$.$

The ability of undefined data to be processed in at least one form

b$.$

The ability for a data to be processed in more than one form

c$.$

The ability of data to be defined in one form

d$.$

The ability of data in a single form, to be reused by all subclasses

Question $8$

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Which of the following is not true about interfaces in Java?