3: Quizzes

Question 1

If A “Is-A” B, what else can we say about the relationship between class A and class B?

1. Class A extends Class B.
2. Class A inherits from Class B.
3. Class A derives from Class B.

Answer 1

All 3.

Question 2

What tool is used to show inheritance or composition relationships among classes.

Answer 2

A class diagram.

Question 3

Which of the following is a specialized version of a class?

1. An ancestor.
2. A subclass.
3. A superclass.
4. class Object.
5. class Class

Answer 3

2

Question 4

Which of the following statements is true?

1. Objects never change the class to which they belong.
2. In some situations, a variable may be bound to different types of objects.
3. The behavior of any object is determined by the object’s class and not by the data type of the variable that references it.

Answer 4

All 3 are true.

Question 5

Given this start to a class definition:

public class Beta extends Alpha {
...
}

What is true about instance variables from Alpha?

1. Class Beta must redeclare all of Alpha’s instance variables.
2. They should not be redeclared in Beta.
3. The Beta class should redeclare only those instance variables from Alpha that it wants.
4. Class Beta should redeclare only the private instance variables from Alpha.

Answer 5

2.

Question 6

If class Fruit is the superclass of class Apple, which of the following is also true?

1. Fruit is the base class of Apple
2. Fruit is the parent class of Apple
3. Apple “Is-A” Fruit

Answer 6

All 3 are true.

Question 7

If a class definition does not include the keyword extends, which of the following is true?

1. The class has no sub class
2. The class has no super class
3. The class implicitly derives from Class.
4. The class implicitly derives from Object.

Answer 7

4.

Question 8

Which of the following things would prevent a method declaration in a subclass from properly overriding an inherited method?

1. not matching the method name
2. not matching the return type
3. not matching the parameter “signature” (number, order and data types of parameters)
4. trying to make a public method private

Answer 8

All of them would prevent a method declaration from properly overriding an inherited method.

Question 9

What is always the very first thing that occurs in the constructor of a derived class?

Answer 9

A call to the superclass constructor is made.

Question 10

Which of the following statements creates a composition (or aggregation) relationship?

1. public class Fun extends Hun { … }
2. return new Fun();
3. if ( myThing instanceof Point ) { … }
4. private Widget myThing;

Answer 10

4.

Question 11

Which Java keyword can be used to access the super class version of an overridden method from within the sub class?

Answer 11

super

Question 12

Given the following code (assume that the statements compile with NO syntax errors):

Red hot = new Red();
Green top = hot;
Orange ocean = new Blue();
hot = ocean;

What is the static type of ‘top’?

Answer 12

Green

Question 13

Given the following code (assume that the statements compile with NO syntax errors):

Red hot = new Red(); 
Green top = hot;
Orange ocean = new Blue();
hot = ocean;

What is the dynamic type of ‘ocean’ after all the statements have been executed?

Answer 13

Blue

Question 14

Given the following code (assume that the statements compile with NO syntax errors):

Red hot = new Red(); 
Green top = hot;
Orange ocean = new Blue(); 
hot = ocean;

What is the dynamic type of ‘hot’ after all the statements have been executed?

Answer 14

Blue

Question 15

What determines which version of an overridden method is executed?

Answer 15

The dynamic type of the variable that acts as the ‘qualifier’ in the method call.

Question 16

What determines which version of an overloaded method is executed?

Answer 16

The data types of the arguments of the method call.

Question 17

A programmer writing code in class Point attempts to override the following inherited method:

public boolean equals( Object o ) { … }

but does not match the method signature exactly. Instead, the programmer uses the following method signature:

public boolean equals( Point p ) { … }

What is the result?

Answer 17

The code compiles, but the inherited method has not been overridden – it has been overloaded instead.

Question 18

Given the following class hierarchy: 
Siamese "Is-A" Feline "Is-A" Mammal "Is-A" LivingThing 

Which of the following is true?

1. ( new Mammal() ) instanceof LivingThing
2. ( new Feline() ) instanceof LivingThing
3. ( new Siamese() ) instanceof LivingThing

Answer 18

All 3 are true.

Question 19

A type cast using reference type is a promise to the compiler that the dynamic type of the expression will conform to the type specified in the cast. What happens if this promise is broken?

Answer 19

A ClassCastException will be thrown.

Question 20

How many different classes can a sub class derive from, using the keyword extends?

Answer 20

Exactly one.

Question 21

If type A conforms to a different type B, then wherever code expects an object of type B, an object of type A may be used.

Answer 21

True.

Question 22

If a class D derives from class S, then objects of type D conform to type S.

Answer 22

True.

Question 23

What is the term for the data type used to declare a reference variable?

Answer 23

Static type.

Question 24

What is the term for the data type of an object bound to a reference variable?

Answer 24

Dynamic type.

Question 25

This term describes when a subclass implements a method with the exact same signature as a method in the super class.

Answer 25

override

Question 26

Which of the following statements tests for CONTENT equality?

1. if ( x == “Hello” ) { … }
2. if ( x.equals( “Hello” ) ) { … }
3. if ( x != “Hello” ) { … }
4. if ( x.contains( “Hello” ) ) { … }

Answer 26

2. if ( x.equals( “Hello” ) ) { … }

Question 27

Which comparison below is acceptable in Java syntax if the following declarations are made?

CSC142Point p1 = new CSC142Point( 3, 4 );
CSC142Point p2 = new CSC142Point( 5, 6 );

1. p1.getX() > p2.getX()
2. p1.setX(5) == p2.setX(5)
3. p1 < p2

Answer 27

1. p1.getX() > p2.getX()

Question 28

Which of the following statements creates a composition (or aggregation) relationship?

1. public doSomething(Boo b){ …}
2. return new Boo();
3. if ( myThing == b ) { … }
4. private Boo myThing;
5. Boo Hoo

Answer 28

4. private Boo myThing;

Question 29

Which of the following things may an abstract class contain in addition to abstract methods?

1. method definitions with implementation
2. instance variable declarations
3. constructor definitions with implementations
4. class constants (final variables)

Answer 29

All 4.

Question 30

What is the difference between an abstract class and a concrete class?

1. An abstract class may NOT be extended.
2. An abstract class may NOT be instantiated.
3. All methods in an abstract class must be abstract.
4. A reference variable cannot have an abstract class as its static type.

Answer 30

2. An abstract class may NOT be instantiated.

Question 31

Which of the following is true about a concrete class?

1. A concrete class may be extended.
2. A concrete class may be instantiated.
3. A concrete may NOT contain abstract methods.
4. All of the above.

Answer 31

4. All of the above.

Question 32

Which of the following is true?

1. A class extends exactly one other class and may implement any number of interfaces.
2. A class may extend at most one concrete class, may extend any number of abstract classes, and may implement any number of interfaces.
3. A class may extend one concrete class and also one abstract class, and may implement any number of interfaces.
4. A class may extend exactly one other class, OR may implement any number of interfaces, but not both.

Answer 32

1. A class extends exactly one other class and may implement any number of interfaces.

Question 33

Given the following declarations,

public class Parent { ... } 
public class Child extends Parent implements Wizard { ... } 
public class Grandchild extends Child { ... }

Which of the following is NOT true?

1. Child “Is-A” Wizard
2. Parent “Is-A” Wizard
3. Grandchild “Is-A” Child
4. Grandchild “Is-A” Parent
5. Grandchild “Is-A” Wizard

Answer 33

2. Parent “Is-A” Wizard

Question 34

In Java a class can inherit members from more than 1 super class. True/false

Answer 34

False

Question 35

Given the following definition:

public class Alpha implements Freezable {…}

And the following client code:

Freezable f = new Alpha();

Which is true?

1. The variable f has static type Freezable and dynamic type Freezable
2. The variable f has static type Freezable and dynamic type Alpha
3. The variable f has static type Alpha and dynamic type Alpha
4. The variable f has static type Alpha and dynamic type Freezable

Answer 35

2. The variable f has static type Freezable and dynamic type Alpha

Question 36

Which of the following creates a new data type?

1. an abstract class definition
2. a concrete class definition
3. an interface definition
4. All of the above.

Answer 36

4. All of the above

Question 37

Which of the following is NOT one of the three categories of collections we have studied?

1. Set
2. Iterator
3. Map
4. List

Answer 37

2. Iterator

Question 38

Which of the following is NOT a wrapper class?

1. String
2. Double
3. Character
4. Integer

Answer 38

1. String

Question 39

Which of the following kinds of things may be stored directly in an ArrayList?

1. object references
2. None of the above
3. Either of these two kinds of data
4. primitive values

Answer 39

1. object references

Question 40

In this declaration:

ArrayList< Point > polygon;

what do we call ‘Point’?

Answer 40

Type argument

Question 41

In this declaration:

ArrayList< Point > polygon;

what is the data type of the variable ‘polygon’?

Answer 41

ArrayList< Point >

Question 42

If this method call:

myList.size()

returns the value 7, what is the range of legal values allowed for the variable x in the following method call?

myList.get( x )

Answer 42

0-6