1Z0-819 Generics & Type Inference 2

Question 1

What is the PECS principle in Java generics?

Accepted Answer

Producer Extends, Consumer Super

Answer

Producer Exceptions, Consumer Static

Answer

Parameter Extends, Consumer Syntax

Answer

Primitive Extends, Collection Super

Question 2

Which operation is valid on a variable declared as List<? extends Number>?

Accepted Answer

Reading elements and treating them as Number type

Answer

Adding an Integer element to the list

Answer

Adding a Double element to the list

Answer

Adding a Number element directly to the list

Question 3

Which operation is valid on a variable declared as List<? super Integer>?

Accepted Answer

Adding an Integer or any of its subtypes to the list

Answer

Reading elements as Integer with guaranteed compile-time type safety

Answer

Adding a String element because the bound accepts any supertype

Answer

Reading elements as a specific Number subtype safely

Question 4

Which of the following correctly declares a type parameter with multiple bounds?

Accepted Answer

public class MyClass>

Answer

public class MyClass>

Answer

public class MyClass>

Answer

public class MyClass>

Question 5

Why does the following code NOT compile? List nums = new ArrayList();

Accepted Answer

Generic types in Java are invariant, so List is not a subtype of List

Answer

ArrayList cannot be assigned to a List variable

Answer

Integer must be explicitly cast to Number before assignment

Answer

The diamond operator must be used on the right-hand side

Question 6

What is the correct signature for Collections.sort() that handles types comparable to their supertypes?

Accepted Answer

public static > void sort(List list)

Answer

public static > void sort(List list)

Answer

public static > void sort(List list)

Answer

public static > void sort(List list)

Question 7

What is the result of calling getClass() on a List and a List at runtime?

Accepted Answer

They return the same class object because type erasure removes parameterized type information

Answer

They return different class objects: the JVM tracks List.class separately from List.class

Answer

getClass() throws an UnsupportedOperationException for generic types

Answer

They both return Object.class because all generic type parameters erase to Object