Question 1

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

Accepted Answer

I is a limitation because of type erasure, where at runtime the generic type information is not available. Therefore, you cannot create an array of a generic type since the compiler cannot guarantee type safety.
II is a limitation because generics only work with reference types and not primitive types. You can use the generic wrapper classes, such as Integer or Double, instead.
III is a limitation because you cannot use the new operator to create a new instance of a generic type. You must use the constructor of the type parameter class, which may require additional type information.

Question 2

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

Accepted Answer

Without a type parameter, the Stack uses Object as the default type. Therefore, the type parameter in this case would be replaced with Object.

Question 3

Consider the following code snippet:
public class LinkedList<E>
{
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?

Accepted Answer

The issue is with the static inner class Node trying to use the generic type E. Since the class is static, it cannot access the generic type parameter of the outer class. Static members belong to the class itself, not to instances of the class, and since the type parameter E is tied to instances, the static inner class cannot use it directly.

Question 4

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

Accepted Answer

A class that requires two generic type variables must have two type arguments provided when creating an instance of the class. Providing zero or one type argument will result in a compilation error. Therefore, the correct options are I and III only.

Question 5

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?

Accepted Answer

The static method replicate cannot refer to type parameters of the generic class LinkedList because it is a static method, and static methods are not part of any instance of a class. Therefore, the type parameter E is not in scope for the replicate method. To fix this, the replicate method should also be declared as a generic method.

Question 6

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 { ...}

Accepted Answer

I is legal because it correctly specifies both generic types required by YourInterface. II is legal because it uses raw types, which is not recommended but still legal in Java. III is incorrect because it does not provide the correct number of generic types for YourInterface.

Question 7

Given an array myArray, which of the following represents an expression to determine the type of the elements of the array?

Accepted Answer

The expression myArray.getClass().getComponentType() returns the type of the elements in the array. This is because getClass() returns the class of the object (in this case, the array), and then getComponentType() returns the type of the array's components (i.e. the type of the elements in the array).

Question 8

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

Accepted Answer

When a generic method accepts an unconstrained argument, the only methods that can be called on that argument are those available in the Object class, as there are no specific type constraints provided.

Question 9

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?

Accepted Answer

The correct code to make a new instance of an object having the same class with a constructor having no arguments is by invoking the getClass() method on the object and then calling newInstance() on the returned Class object. Therefore, option D is the correct choice. Option A is incorrect because the newInstance() method cannot be called directly on the Object class. Option B is incorrect because it calls getClass() on the return value of newInstance() method, which will return the Class object of the new instance and not the instance itself. Option C is incorrect because it only returns the class of myObject and not a new instance.

Question 10

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

Accepted Answer

The type erasure process is necessary for both I and II. The Java virtual machine cannot work with generic types and therefore requires the type erasure process to replace generic types with their bounds or Object types during compilation. To maintain compatibility with older versions of Java, type erasure is also necessary as generic types were not available in older versions of Java. Choice III, on the other hand, is not correct as generics do work with primitives and can be used with wrapper classes.

Question 11

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.

Accepted Answer

III only. Generic types in Java have certain restrictions, and one of the key restrictions is that you cannot directly create arrays of a generic type due to type erasure and the way generics are implemented in Java. The other statements (I and II) are incorrect; you can use the assignment operator = to assign one generic object to another if they are of the same generic type, and you can use the == operator to compare two generic object references to see if they refer to the same instance.

Question 12

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

Accepted Answer

The type parameter in Stack is replaced with String, as specified in the declaration "private Stack myStack = new Stack<>();".

Question 13

Consider the following code snippet:
public class LinkedList<E>
{
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?

Accepted Answer

The issue is with declaring a static variable `defaultValue` with the generic type `E`. Static fields are shared among all instances of a class, regardless of the generic type parameter. Since the type parameter `E` can differ between different instances of `LinkedList`, a static field cannot be declared with a type parameter `E`.

Question 14

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

Accepted Answer

Generic code cannot declare static variables, static methods, or static inner classes of a generic type.

Question 15

Consider the following code snippet:
public static <E extends Measurable> E min(E[] objects)
Which of the following represents the result of type erasure on this code?

Accepted Answer

The result of type erasure on the given code would be "public static Measurable min(Measurable[] objects)". This is because the type parameter "E" extends the Measurable interface, so after type erasure, the method's signature would become "public static Measurable min(Measurable[] objects)". This means that the method takes an array of Measurable objects and returns a Measurable object (which is the minimum of the array).

Quiz 18: Generic Classes

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

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

Consider the following code snippet: public class LinkedList<E> { 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?

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

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

Given an array myArray, which of the following represents an expression to determine the type of the elements of the array?

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

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?

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

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.

Given the following declaration, what is the type parameter in Stack<E> replaced with? private Stack<String> myStack = new Stack<>() ;

Consider the following code snippet: public class LinkedList<E> { 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?

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

Consider the following code snippet: public static <E extends Measurable> E min(E[] objects) Which of the following represents the result of type erasure on this code?