1Z0-819 Generics & Type Inference

Question 1

What does type erasure mean in the context of Java generics?

Accepted Answer

Generic type parameters are converted to their bounds (or Object) in compiled bytecode

Answer

Generic type information is retained at runtime for reflection purposes

Answer

Generic types are validated at runtime by the JVM

Answer

Type erasure removes all Object references from generic classes

Question 2

Which of the following correctly declares a generic method in Java?

Accepted Answer

public <T> T getValue() { return null; }

Answer

public T <T> getValue() { return null; }

Answer

public generic<T> T getValue() { return null; }

Answer

public T getValue<T>() { return null; }

Question 3

What does the diamond operator <> accomplish when used in Java?

Accepted Answer

Instructs the compiler to infer the type parameter from the surrounding context

Answer

Declares an unbounded wildcard type for any collection

Answer

Creates an empty generic collection with no element type

Answer

Specifies that a class implements a generic interface

Question 4

Which statement about using raw types in Java is TRUE?

Accepted Answer

Raw types bypass generic type checking and can lead to ClassCastException at runtime

Answer

Raw types are fully type-safe because they default to Object

Answer

Using raw types generates compile-time errors in modern Java

Answer

Raw types are recommended when writing new code for maximum flexibility

Question 5

Given: List strList = new ArrayList<>(); Which assignment is valid?

Accepted Answer

List<? extends String> extList = strList;

Answer

List<Object> objList = strList;

Answer

ArrayList<Object> arrList = strList;

Answer

Collection<Object> colList = strList;

Question 6

Which of the following creates an illegal parameterized array in Java?

Accepted Answer

List[] arr = new ArrayList[5];

Answer

Object[] arr = new String[5];

Answer

List[] arr = new ArrayList[5];

Answer

String[] arr = new String[5];

Question 7

What is the primary benefit of using generics over using Object as a parameter type?

Accepted Answer

Generics provide compile-time type safety and eliminate the need for explicit casting

Answer

Generics allow the use of primitive types directly without autoboxing

Answer

Generics improve runtime performance by skipping JVM type checks entirely

Answer

Generics allow creating instances of type parameters using new T()