Deck 18: Generic Classes

Question 1

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

Answer 1

Box

Question 2

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<>();

Answer 2

Box box = new Box<>();

Question 3

Which of the following statements about generic programming is NOT correct?
A.Generic programming can be achieved by using type parameters.
B.Generic classes use type parameters to achieve genericity.
C.To achieve genericity through inheritance, you must include type parameters to specify the type of object to be processed.
D.Generic programming can be achieved by using inheritance.

Answer 3

To achieve genericity through inheritance, you must include type parameters to specify the type of object to be processed.

Question 4

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 parameter
C.it is a cast
D.it is an instance variable

Question 5

In Java, generic programming can be achieved with ____.
A.polymorphism
B.arrays
C.encapsulation
D.inheritance

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

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.ClassCastException
B.Exception
C.IndexOutOfBoundsException
D.NoSuchElementException

Question 8

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

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 and III only
B.III only
C.I only
D.II only

Question 10

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

Question 11

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

Question 12

Which Java technique(s) allows generic programming?
I type variables
II primitive types
III inheritance
A.I only
B.I and III only
C.III only
D.II only

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 = box.getData();
A.no error
B.compiler warning
C.run-time error
D.compiler error

Question 14

Consider the following code snippet:
ArrayList arr = new ArrayList<>();
String element = arr.get(0);
Is there an error in this code?
A.No run-time error or compile-time errors will occur.
B.Yes, a compile-time error will occur because you cannot create an ArrayList of type Double.
C.Yes, a run-time error will occur because a Double value cannot be cast to a String value.
D.Yes, a compile-time error will occur because you cannot assign a Double value to a String variable.

Question 15

Consider the following code snippet: Which of the above lines will cause a compile-time error?
A.Line 2
B.Line 3
C.Line 4
D.Line 1

Question 16

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

Question 17

Which of the following statements about generic programming is NOT correct?
A.Type parameters can be instantiated with wrapper class types.
B.Type parameters can be instantiated with class types.
C.Type parameters can be instantiated with primitive data types.
D.Type parameters can be instantiated with interface types.

Question 18

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.correct, but unnecessary cast
C.correct, with necessary cast
D.run-time error

Question 19

Which of these Java library classes are implemented using type variables?
I HashMap
II LinkedList
III ArrayList
A.I, II and III
B.II and III only
C.I and III only
D.I and II only

Question 20

Which of the following statements about using generic programming is NOT correct?
A.Using type parameters will potentially avoid some class cast exceptions that may occur when using collections without type parameters.
B.Using type parameters makes generic code easier to read and understand.
C.Type parameters cannot be used with interfaces.
D.Using type parameters makes generic code safer.

Question 21

Which argument type cannot be passed to generic methods?
I Object
II GUI components
III primitive
A.III only
B.I only
C.II only
D.I and III only

Question 22

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 only
B.I, II and III
C.II and III only
D.none are necessary

Question 23

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 e)
II public static E myMethod(E e)
III public E myMethod(E e)
A.I only
B.I and III only
C.III only
D.II only

Question 24

The type variables in HashMap in the standard library mnemonically represent ____.
A.kernel and vector
B.String and Vector
C.kind and variable
D.key and value

Question 25

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};
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)
II public static E[] makeArray(int[] a)
III public static Integer[] makeArray(E[] a)
A.II and III only
B.I and III only
C.I and II only
D.I only

Question 26

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 only
B.III only
C.II only
D.II and III only

Question 27

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

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

Question 28

What is the best technique for overcoming the restriction for the use of primitives, such as int, in generic classes and methods?
A.do not use generic methods when using primitives
B.use String and decode values with a method such as Integer.parseInt
C.use of wrapper classes
D.use of the Object type

Question 29

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

Question 30

Which of the following statements about generic methods is NOT correct?
A.Supply the type parameters of a generic method between the modifiers and the method return type.
B.Generic methods can be static methods.
C.You need not instantiate the type parameter when calling a generic method.
D.You can replace type parameters with primitive types.

Question 31

Determine the output of the MyLinkedList generic class code below when the main method executes.
public class MyLinkedList
{
private MyNode first;
public MyLinkedList(E 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());
}
}
A.compiler error is generated by first = new MyNode();
B.no output
C.List first element = Hello
D.List first element = null

Question 32

Given the following generic method, which of the following CANNOT be the return type?
public static > E max(E[] a) { ...}
I String
II Integer
III double
A.I only
B.I and III only
C.III only
D.II only

Question 33

Select the correct header for this generic print method.
public static void print(E[] a)
{
for (int i = 0; i < a.length; i++)
{
System.out.println(a[i] + " ");
}
}
A.The header is correct
B.public void print(E [] a)
C.public static void print(E a)
D.public static void print(E[] a)

Question 34

Which of the following statements about generic methods is correct?
A.The generic type parameter of a generic method designates the method's return type.
B.A generic method must have a generic type parameter.
C.When calling a generic method, you need to instantiate the type parameters.
D.A generic method must reside in a generic class.

Question 35

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.none are restrictions
B.II and III only
C.I and II only
D.I only

Question 36

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.II and III only
B.II only
C.III only
D.I only

Question 37

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.II and III only
B.I and II only
C.I, II and III
D.I only

Question 38

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

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

Question 39

Given the following generic method, which of the following is a possible return type?
public static > E max(E[] a) { ...}
I String
II Object
III Double
A.I only
B.I and III only
C.II only
D.I and II only

Question 40

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.II only
B.I only
C.III only
D.II and III only

Question 41

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 only
B.II only
C.II and III only
D.III only

Question 42

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 43

What does it mean when the syntax ? extends D is used?
A.Any subclass of D may be used.
B.Any superclass of D may be used.
C.This indicates a wildcard with an upper bound.
D.Any subclass or superclass of D may be used.

Question 44

To maintain compatibility with pre-generic Java, type parameters are replaced by ordinary types called ____.
A.raw types
B.primitives
C.generics
D.Object

Question 45

Consider the following code snippet:
public static void reverse(List list) { ...}
Which of the following statements about this code is correct?
A.This code is illegal.
B.This is an example of a wildcard with an upper bound.
C.This is an example of a wildcard with a lower bound.
D.This is an example of an unbounded wildcard.

Question 46

Suppose a linked-list class called MyLinkedList with a generic E type has been instantiated 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 only
B.I and II only
C.II and III only
D.I, II, and III

Question 47

Which of the following statements about the Java virtual machine is correct?
A.The Java virtual machine always replaces type parameters with their lower bounds.
B.The Java virtual machine always replaces type parameters with their upper bounds.
C.The Java virtual machine replaces type parameters with their bounds or with type Object.
D.The Java virtual machine always replaces type parameters with type Object.

Question 48

Which of the following is not a wildcard type?
A.? sub B
B.? extends B
C.? super B
D.?

Question 49

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

Question 50

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

Question 51

Which of the following satisfies the wildcard ? extends Component?
A.Scanner
B.Color
C.String
D.JButton

Question 52

Which of the following satisfies the wildcard ? extends Object?
I String
II JComponent
III Scanner
A.I and II only
B.I only
C.II only
D.I, II and III

Question 53

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

Question 54

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.There is no relationship between ArrayList and ArrayList
D.ArrayList extends ArrayList.

Question 55

Consider the following code snippet:
public static void reverse(List list) { ...}
Which of the following statements about this code is correct?
A.This code is illegal.
B.This is an example of an unbounded wildcard.
C.This is an example of a wildcard with an upper bound.
D.This is an example of a wildcard with a lower bound.

Question 56

Which of the following satisfies the wildcard ? super Object?
A.JComponent
B.None satisfy this wildcard.
C.Scanner
D.String

Question 57

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

Question 58

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 void fun(Object[] t) { ...}
C.public static void fun(Object t) { ...}
D.public static

Question 59

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 60

What does it mean when the syntax ? super D is used?
A.Any superclass of D may be used.
B.This indicates a wildcard with a lower bound.
C.Any subclass or superclass of D may be used.
D.Any subclass of D may be used.

Question 61

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 only
B.I, II and III
C.II only
D.III only

Question 62

Given the following declaration, what is the type parameter in Stack replaced with?
private Stack myStack = new Stack();
A.String
B.Object
C.it is a compiler error
D.int

Question 63

Consider the following code snippet:
public class LinkedList
{
private E defaultValue;
public void add(E value, int n) { ...}
private static class Node { public E 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 a static inner class in a generic class as shown.

Question 64

If a class requires two generic type variables, how many can you legally provide in Java?
I 0
II 1
III 2
A.I and II only
B.I and III only
C.I only
D.II only

Question 65

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

Question 66

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 and III only
B.III only
C.I only
D.I and II only

Question 67

Given an array myArray, which of the following represents an expression to determine the type of the elements of the array?
A.myArray.getClass().getComponentType()
B.myArray.getComponentType().getClass()
C.myArray.getClass().getElementType()
D.myArray[0].getClass()

Question 68

Suppose a generic method accepts a generic unconstrained argument p.What restrictions are placed on p by the compiler?
A.There are no restrictions.
B.Can only execute methods from its own class.
C.Can only execute Object class methods.
D.Can not execute any methods.

Question 69

Given an object myObject, which of the following represents the correct code to make a new instance of an object having the same class, assuming that the class has a constructor with no arguments?
A.Object newObject = myObject.newInstance();
B.Object newObject = myObject.newInstance().getClass();
C.Object newObject = myObject.getClass();
D.Object newObject = myObject.getClass().newInstance();

Question 70

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.II only
B.I and III only
C.I and II only
D.I only

Question 71

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.II only
B.III only
C.I only
D.I and III only

Question 72

Given the following declaration, what is the type parameter in Stack replaced with?
private Stack myStack = new Stack<>();
A.Object
B.String
C.Stack
D.int

Question 73

Consider the following code snippet:
public class LinkedList
{
private static E defaultValue;
public void add(E value, int n) { ...}
private class Node { public String data; public Node next;}
...
}
What is wrong with this code?
A.Cannot pass a generic type as an argument to a method as shown.
B.Cannot have an inner class in a generic class as shown.
C.Cannot declare the variable defaultValue as a generic data type.
D.Cannot declare the variable defaultValue as static.

Question 74

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.II only
B.I only
C.I and II only
D.I, II, and III

Question 75

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