Deck 18: Generic Classes

Question 1

Which of the following statements about generic programming is NOT correct?

A) Type parameters can be instantiated with class types.
B) Type parameters can be instantiated with interface types.
C) Type parameters can be instantiated with primitive data types.
D) Type parameters can be instantiated with wrapper class types.

Answer 1

C

Question 2

Consider the following code snippet:
ArrayList arr = new ArrayList();
String element = arr.get(0);
Is there an error in this code?

A) Yes, a run-time error will occur because a Double value cannot be cast to a String value.
B) Yes, a compile-time error will occur because you cannot assign a Double value to a String variable.
C) No run-time error or compile-time errors will occur.
D) You cannot create an arraylist of type Double.

Answer 2

B

Question 3

Consider the following code snippet:
ArrayList coins1 = new ArrayList(); //Line 1
LinkedList coins2 = new LinkedList(); //Line 2
Coins1.add("my penny"); //Line 3
Coins2.addFirst("my penny"); //Line 4
Which of the above lines will cause a compile-time error?

A) Line 1
B) Line 2
C) Line 3
D) Line 4

Answer 3

C

Question 4

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box() { . . . }
Public void insert(E value) { . . . }
Public E getData(){ . . . }
}
What will result from executing the following code?
Box box = new Box();
) . .
Box)insert("blue Box");
String b = box.getData();

A) compiler error
B) run-time error
C) no error
D) compiler warning

Question 5

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box() { . . . }
Public void insert(E value) { . . . }
Public E getData(){ . . . }
}
What will result from the following code?
Box box = new Box();
) . .
Box)insert("blue Box");
Double myDouble = (Double) box.getData();

A) compiler error
B) run-time error
C) correct, but unnecessary cast
D) correct, with necessary cast

Question 6

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box(){ . . . }
Public void insert(E value) { . . . }
}
Which of the following is a valid Box object instantiation?
I Box

Question 7

Which of the following statements about using generic programming is NOT correct?

A) Using type parameters makes generic code safer.
B) Using type parameters makes generic code easier to read and understand.
C) Using type parameters will potentially avoid some class cast exceptions that may occur when using collections without type parameters.
D) Type parameters cannot be used with interfaces.

Question 8

Which is the purpose of the element in the class declaration below?
Public class Thing
{
Public Thing() { . . . }
}

A) declares that only instances of E class can be stored
B) it is a type variable
C) it is an instance variable
D) it is a cast

Question 9

Which Java generic programming technique(s) requires the programmer to use casting to access variables stored as Object types?
I type variables
II primitive types
III inheritance

A) I
B) II
C) III
D) I and III

Question 10

Consider the following code snippet:
ArrayList coins1 = new ArrayList(); //Line 1
LinkedList coins2 = new LinkedList(); //Line 2
Coins1.add("my penny"); //Line 3
Coins2.addFirst("my penny"); //Line 4
Which of the above lines will cause a run-time error when the object is retrieved elsewhere in the program?

A) Line 1
B) Line 2
C) Line 3
D) Line 4

Question 11

Consider the following code snippet:
ArrayList accounts1 = new ArrayList(); //Line 1
LinkedList accounts2 = new LinkedList(); //Line 2
Accounts1.add("my Salary"); //Line 3
Accounts2.addFirst("my Salary"); //Line 4
Which of the above lines will cause a compile-time error?

A) Line 1
B) Line 2
C) Line 3
D) Line 4

Question 12

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box() { . . . }
Public void insert(E value) { . . . }
Public E getData() { . . . }
}
What will result from executing the following code?
Box box = new Box();
Box b = (Box) box.getData();

A) compile-time error
B) run-time error
C) correct generic assignment
D) compile-time warning

Question 13

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box(){ . . . }
Public void insert(E value) { . . . }
Public E getData() { . . . }
}
What will result from executing the following code?
Box box = new Box();
) . .
Box)insert("blue Box");
String b = (String) box.getData();

A) compiler error
B) run-time error
C) correct, but unnecessary cast
D) correct, with necessary cast

Question 14

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box(){ . . . }
}
Which of the following is a valid Box object instantiation?

A) Box box = new Box;
B) Box box = new Box();
C) Box box = new Box();
D) Box box = new Box();

Question 15

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box() { . . . }
Public void insert(E value) { . . . }
}
What will result from executing the following code?
Box box = new Box();
Box)insert("blue Box");

A) compile-time error
B) run-time error
C) correct generic assignment
D) compile-time warning

Question 16

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box() { . . . }
}
Which of the following choices is a specific type of the generic Box class?

A) Box
B) Box
C) Box
D) Box

Question 17

Which Java technique(s) allows generic programming?
I type variables
II primitive types
III inheritance

A) I
B) II
C) III
D) I and III

Question 18

Which of the following statements about generic programming is NOT correct?

A) Generic classes use type parameters to achieve genericity.
B) Generic programming can be achieved by using inheritance.
C) Generic programming can be achieved by using type parameters.
D) To achieve genericity through inheritance, you must include type parameters to specify the type of object to be processed.

Question 19

Consider the following code snippet:
ArrayList accounts1 = new ArrayList(); //Line 1
LinkedList accounts2 = new LinkedList(); //Line 2
Accounts1.add("my Salary"); //Line 3
Accounts2.addFirst("my Salary"); //Line 4
Which of the above lines will cause a run-time error when the object is retrieved elsewhere in the program?

A) Line 1
B) Line 2
C) Line 3
D) Line 4

Question 20

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box(){ . . . }
Public void insert(E value) { . . . }
Public E getData(){ . . . }
}
What will result from executing the following code?
Box box = new Box();
) . .
Box)insert("blue Box");
String b = (Object) box.getData();

A) compiler error
B) run-time error
C) correct, but unnecessary cast
D) correct, with necessary cast

Question 21

Consider the following code snippet:
Public static void print(E []
A) {
For (int i = 0; i < a.length; i++)
{
System.out.println(a[i] + " ");
}
}
Int[] a = {3,6,5,7,8,9,2,3};
String[] s = {"happy","cat","silly","dog"};
Boolean[] b = {true, true, false};
Which of the following are correct calls to this generic print method?
I print(a);
II print(s);
III print(b);

A) I
B) I and II
C) II and III
D) I, II and III

Question 22

Which of these Java library classes are implemented using type variables?
I HashMap
II LinkedList
III ArrayList

A) I and II
B) II and III
C) I and III
D) I, II and III

Question 23

Deep Check
Select the correct header for this generic print method.
Public static void print(E[]
A)
A)
A)
A) {
For (int i = 0; i < a.length; i++)
{
System.out.println(a[i] + " ");
}
}

A) public static void print(E[]

Question 24

The type variables in HashMap in the standard library mnemonically represent ____.

A) kernel and vector
B) key and value
C) kind and variable
D) String and Vector

Question 25

Consider our own generic class MyLinkedList shown below. It has a private Node class, and it implements the standard Java ListIterator generic interface.
Public class MyLinkedList
{
Private MyNode first;
) . .
Private class MyNode
{
Private E data;
Private MyNode next;
}
Private class MyIterator implements ListIterator
{
) . .
}
}
Which of the following statements apply?
I the code is correct
II change to private class MyIterator implements ListIterator
III change to private class MyNode

A) I
B) II
C) III
D) II and III

Question 26

Determine the correctness of the MyLinkedList generic class code below.
Public class MyLinkedList
{
Private MyNode first;
Public E getFirst() { return first.data; }
Private class MyNode
{
Private E data;
Private MyNode next;
}
}

A) MyNode cannot refer to type variable E
B) first.data will cause a compiler error
C) the inner class MyNode cannot be private
D) the code is correct

Question 27

Which argument type cannot passed to generic methods?
I Object
II GUI components
III primitive

A) I
B) II
C) III
D) I and III

Question 28

Which of the following statements about generic methods is correct?

A) A generic method must reside in a generic class.
B) A generic method must have a generic type argument.
C) A generic method must have a generic type parameter.
D) The generic type parameter of a generic method designates the method's return type.

Question 29

Determine the output of the MyLinkedList generic class code below when the main method executes.
Public class MyLinkedList
{
Private MyNode first;
Public MyLinkedList(E

A) List first element = Hello
B) List first element = null
C) compiler error is generated by first = new MyNode();
D) no output
E) {
First = new MyNode();
First.data = e;
First.next = null;
}
Public E getFirst() { return first.data; }
Private class MyNode
{
Private E data;
Private MyNode next;
}
Public static void main(String[] args)
{
MyLinkedList list = new MyLinkedList("Hello");
System.out.println("List first element = " + list.getFirst());
}
}

Question 30

Deep Check
Consider the following code snippet:
Public static void print(E[]
A)
A) II public static E[] makeArray(int[]
A) III public static Integer[] makeArray(E[]
A) {
For (int i = 0; i < a.length; i++)
{
System.out.println(a[i] + " ");
}
}
Int[] a = {3,6,5,7,8,9,2,3};
Print(makeArray(a));
Assume that the method call to print(makeArray(a)) works correctly by printing the int array a. Which of the following headers for the makeArray method will make this possible?
I public static Integer[] makeArray(int[]

A) I

Question 31

In Java, generic programming can be achieved with ____.

A) encapsulation
B) inheritance
C) polymorphism
D) arrays

Question 32

Consider the following code snippet:
Public class Box
{
Private E data;
Public Box(){ . . . }
Public void insert(E value) { . . . }
Public E getData(){ . . . }
}
What specific exception will be thrown when the following code executes?
Box box = new Box();
) . .
Box)insert("blue Box");
Double myDouble = (Double) box.getData();

A) Exception
B) NoSuchElementException
C) IndexOutOfBoundsException
D) ClassCastException

Question 33

Which of the following statements regarding restrictions for generic methods are true?
I Generic methods must be declared inside a generic class.
II Generic methods must be static.
III Generic methods may only have one generic parameter.

A) I
B) I and II
C) II and III
D) none are restrictions

Question 34

What is the best technique for overcoming the restriction for the use of primitives, such as int, in generic classes and methods?

A) use of the Object type
B) use of wrapper classes
C) use String and decode values with a method such as Integer.parseInt
D) do not use generic methods when using primitives

Question 35

Deep Check
Which of the following headers for a generic method myMethod allows the actionPerformed method from the ActionListener class to be called?
I public static E myMethod(E

A) I
B) II
C) III
D) I and III
E)

Question 36

An inner helper class, such as a TreeNode inside the generic BinaryTree class, must meet which of the following criteria?
I be public
II be private
III be declared as generic

A) I and III
B) II and III
C) I, II and III
D) none are necessary

Question 37

Consider the following declaration:
LinkedList list = new LinkedList();
This declaration implies that the LinkedList class could begin with which of the following code statements?
I public class LinkedList { . . . }
II public class LinkedList { . . . }
III public class LinkedList { . . . }

A) I
B) II
C) III
D) II and III

Question 38

What is known for certain about a type parameter when a method constrains it as follows?

A) it is either a MouseListener or MouseMotionListener implementer
B) it implements MouseListener and MouseMotionListener
C) it is of type MouseEvent
D) the code is illegal; the & symbol should read and

Question 39

What is known for certain about Visualizer when a method constrains its type parameter as follows?

A) Visualizer must refer to a class
B) Visualizer must refer to an interface
C) Visualizer can refer to either an interface or a class
D) Visualizer is another generic type

Question 40

Which of the following statements about generic methods is correct?

A) You must instantiate the type parameter when calling a generic method.
B) You must specify which type to use when calling a generic method.
C) Generic methods cannot be static methods.
D) You cannot replace type parameters with primitive types.

Question 41

Consider the following code snippet:
Public static > E min(ArrayList objects)
What can we conclude about the return type of this method?

A) The return type is a class that extends Comparable.
B) The return type is a class that implements Comparable.
C) The return type is an array list of generic objects.
D) The return type is a subclass of the ArrayList class.

Question 42

Which of the following is not a wildcard type?

A) ?
B) ? super B
C) ? sub B
D) ? extends B

Question 43

Consider the following code snippet:
Public class SavingsAccount extends BankAccount { . . . }
Public class CheckingAccount extends BankAccount { . . . }
) . .
SavingsAccount[] savingsAccounts = new SavingsAccount[100]; //Line 1
BankAccount bankAccounts = savingsAccounts; //Line 2
BankAccount myAccount = new CheckingAccount(); //Line 3
BankAccounts[0] = myAccount; //Line 4
Which of the following statements regarding this code is correct?

A) Line 2 will cause a compile-time error.
B) Line 2 will cause a run-time error.
C) Line 4 will cause a compile-time error.
D) Line 4 will cause a run-time error.

Question 44

What does it mean when the syntax ? extends D is used?

A) Any superclass of D may be used.
B) Any subclass of D may be used.
C) Any subclass or superclass of D may be used.
D) This indicates a wildcard with an upper bound

Question 45

Consider the following code snippet that declares the GraduateStudent class:
Public GraduateStudent extends Student { . . .}
Which of these statements are false?
I GraduateStudent is a subclass of Student
II Stack is a subclass of Stack
III Stack is a subclass of Stack

A) I
B) II
C) III
D) II and III

Question 46

Which of the following satisfies the wildcard ? extends Component?

A) String
B) Scanner
C) JButton
D) Color

Question 47

Which of the following satisfies the wildcard ? super Object?

A) String
B) JComponent
C) Scanner
D) none satisfy this wildcard

Question 48

Given the following generic method, which of the following is a possible return type?
Public static E max(E[]
A) I

A) { . . . }
I String
II Object
III Double
B) II
C) I and II
D) I and III

Question 49

Which code is the equivalent of the following method header?
Public static void abc(Stack stack) { . . . }
I public static void abc(Stack stack) { . . . }
II public static

Question 50

Consider the following class declaration:
Public class SavingsAccount extends BankAccount { . . . }
Which of the following statements about these classes is correct?

A) ArrayList is a subclass of ArrayList.
B) ArrayList is a subclass of ArrayList.
C) ArrayList extends ArrayList.
D) There is no relationship between ArrayList and ArrayList

Question 51

Consider the following code snippet:
Public static void reverse(List list) { . . . }
This method declaration is equivalent to which of the following declarations?

A) public static void reverse(List list) { . . . }
B) public static void reverse(List list) { . . . }
C) public static void reverse(List list) { . . . }
D) public static void reverse(List list) { . . . }

Question 52

Consider the following code snippet:
Public static void reverse(List list) { . . . }
Which of the following statements about this code is correct?

A) This is an example of a wildcard with an upper bound.
B) This is an example of a wildcard with a lower bound.
C) This is an example of an unbounded wildcard.
D) This code is illegal.

Question 53

What does the following code snippet mean:
& Measurable>

A) The class represented by E extends Comparable and Measurable.
B) The class represented by E implements Comparable and Measurable.
C) The class represented by E implements Comparable and extends Measurable.
D) The class represented by E extends Comparable and implements Measurable.

Question 54

Suppose a linked-list class with a generic E type has been constructed with a java.awt.Component type variable. Consider its instance method locate with the following header:
Public void locate(MyLinkedList) { . . . }
Which type cannot be passed to method locate?
I MyLinkedList
II MyLinkedList
III MyLinkedList

A) I
B) I and II
C) II and III
D) all can be passed to locate

Question 55

What does it mean when the syntax ? super D is used?

A) Any superclass of D may be used.
B) Any subclass of D may be used.
C) Any subclass or superclass of D may be used.
D) This indicates a wildcard with a lower bound

Question 56

Which of the following satisfies the wildcard ? extends Object?
I String
II JComponent
III Scanner

A) I
B) II
C) I and II
D) I, II and III

Question 57

Consider the following code snippet in the LinkedList class:
Public void addAll(LinkedList other)
{
ListIterator iter = other.listIterator();
While (iter.hasNext())
{
Add(iter.next());
}
}
Which of the following statements about this code is correct?

A) You must supply a specific type for the element type of other.
B) For the element type of other, you must supply a type that is a subtype of E.
C) For the element type of other, you must supply a type that is a supertype of E.
D) For the element type of other, you must supply a type that is either a subtype or a supertype of E.

Question 58

Given the following generic method, which of the following CANNOT be the return type?
Public static E max(E[]
A) I

A) { . . .}
I String
II Integer
III double
B) II
C) III
D) I and III

Question 59

Consider the following code snippet:
Public static void reverse(List list) { . . . }
Which of the following statements about this code is correct?

A) This is an example of a wildcard with an upper bound.
B) This is an example of a wildcard with a lower bound.
C) This is an example of an unbounded wildcard.
D) This code is illegal.

Question 60

Consider the following code snippet:
Public static void reverse(List list) { . . . }
Which of the following statements about this code is correct?

A) This is an example of a wildcard with an upper bound.
B) This is an example of a wildcard with a lower bound.
C) This is an example of an unbounded wildcard.
D) This code is illegal.

Question 61

Consider the following code snippet:
Public static void fun(T[] t) { . . . }
Erasure by the compiler of method fun will generate which result?

A) public static void fun(Object[] t) { . . . }
B) public static

Question 62

Erasure of types limits Java code somewhat with generics. Which of the following are limitations of generic code?
I cannot instantiate a type variable
II cannot return a type variable
III cannot pass a type variable

A) I
B) II
C) III
D) II and III

Question 63

Generics limit Java code somewhat. Which of the following are limitations of generic code?
I cannot declare static variables of a generic type
II cannot declare static methods of a generic type
III cannot declare static inner classes of a generic type

A) I
B) II
C) I and II
D) I, II, and III

Question 64

Consider the following code snippet:
Public class LinkedList
{
Private E defaultValue;
Public static List replicate(E value, int n) { . . . }
Private class Node { public String data; public Node next;)
) . .
}
What is wrong with this code?

A) Cannot declare the variable defaultValue as a generic type.
B) Cannot pass a generic type as an argument to a method.
C) Cannot have a static method in a generic class as shown.
D) Cannot have an inner class in a generic class.

Question 65

Consider the following code snippet:
Public static E min(E[] objects)
Which of the following represents the result of type erasure on this code?

A) public static Measurable E min(Measurable E[] objects)
B) public static Measurable min(Measurable[] objects)
C) public static E min(Measurable E[] objects)
D) This code is illegal and type erasure will not occur.

Question 66

Which of the following necessitates the type erasure process?
I The Java virtual machine does not work with generic types
II To maintain backward compatibility to older versions of Java
III Generics do not work with primitives

A) I
B) II
C) I and II
D) I and III

Question 67

What is the result when a program constructs a generic class without passing a type variable, as in the following code?
Stack stack = new Stack();
I the program will compile and run
II the compiler will issue an error
III the compiler will issue a warning

A) I
B) II
C) III
D) I and III

Question 68

Given the following declaration, what is the type parameter in Stack replaced with?
Private Stack myStack = new Stack();

A) String
B) Object
C) int
D) Stack

Question 69

To maintain compatibility with pre-generic Java, type parameters are replaced by ordinary types called ____.

A) primitives
B) raw types
C) Object
D) generics

Question 70

Consider the following code snippet:
Public class LinkedList
{
Private E defaultValue; //Line 1
Public void add(E value, int n) { . . . } //Line 2
Private static class Node { public E data; public Node next;)//Line 3
) . .
}
What is wrong with this code?

A) Cannot declare the variable defaultValue as a generic type.
B) Cannot pass a generic type as an argument to a method.
C) Cannot have a static method in a generic class as shown.
D) Cannot have a static inner class in a generic class as shown.

Question 71

Given the following declaration, what is the type parameter in Stack replaced with?
Private Stack myStack = new Stack();

A) String
B) Object
C) int
D) it is a compiler error

Question 72

Suppose a generic method accepts a generic unconstrained argument p. What restrictions are placed on p by the compiler?

A) Can only execute Object class methods.
B) Can only execute methods from its own class.
C) Can not execute any methods.
D) There are no restrictions.

Question 73

If a class requires two generic type variables, how many can you legally provide in Java?
I 0
II 1
III 2

A) I
B) II
C) I and II
D) I and III

Question 74

Consider the following code snippet:
Public interface MyInterface { . . . }
Public interface YourInterface extends MyInterface { . . . }
Which of these are legal class declarations?
I public class SomeClass implements YourInterface { . . . }
II public class SomeClass implements YourInterface { . . . }
III public class SomeClass implements YourInterface { . . . }

A) I
B) III
C) I and II
D) I and III

Question 75

Generics limit Java code somewhat. Which of the following are considered limitations of generic code?
I cannot have an array of a generic type
II cannot have primitive type variables
III cannot construct an object of a generic type

A) I
B) II
C) III
D) I, II and III

Question 76

Which of the following are restrictions of Java generic programming?
I You cannot use the assignment operator = to assign one generic object to another.
II You cannot use the == operator to compare two generic objects.
III You cannot construct arrays of generic types.

A) I
B) II
C) III
D) I and III

Question 77

Which of the following statements about the Java virtual machine is correct?

A) The Java virtual machine always replaces type parameters with their upper bounds.
B) The Java virtual machine always replaces type parameters with their lower bounds.
C) The Java virtual machine always replaces type parameters with type Object.
D) The Java virtual machine replaces type parameters with their bounds or with type Object.

Question 78

Consider the following code snippet:
Public class LinkedList
{
Private static E defaultValue; //Line 1
Public void add(E value, int n) { . . . } //Line 2
Private class Node { public String data; public Node next;)//Line 3
) . .
}
What is wrong with this code?

A) Cannot declare the variable defaultValue as static.
B) Cannot pass a generic type as an argument to a method as shown.
C) Cannot have an inner class in a generic class as shown.
D) Cannot declare the variable defaultValue as a generic data type.