1Z0-811 Core Java API

Question 1

What is the output of the following code? import java.util.*;
public class Test {
public static void main(String[] args) {
List list = Arrays.asList("A", "B", "C");
list.add("D");
}
}

Accepted Answer

Compilation error

Answer

The `Arrays.asList()` method returns a fixed-size `List` backed by the original array. This list does not support structural modifications such as adding or removing elements. Attempting to call the `add()` method on this type of list will result in an `UnsupportedOperationException` at runtime, not a compilation error, because the `add` method is syntactically valid but semantically unsupported by the specific list implementation.

Question 2

Which interface in the Java Collections Framework represents a collection of elements that allows for duplicates and maintains insertion order?

Accepted Answer

List

Answer

The `List` interface in the Java Collections Framework represents an ordered collection (sequence) of elements. It explicitly allows for duplicate elements and maintains the insertion order of elements. In contrast, `Set` does not allow duplicates, `Queue` maintains order for processing, and `Map` stores key-value pairs.

Question 3

Which of the following classes is part of the Java Collections Framework and provides constant-time performance for the basic operations?

Accepted Answer

HashSet

Answer

The `HashSet` class provides constant-time performance (on average) for basic operations like `add`, `remove`, and `contains`. This efficiency is achieved by using a hash table for storage. `LinkedList`, `ArrayList`, and `TreeSet` have different performance characteristics, typically involving O(n) or O(log n) for some operations.

Question 4

How does the Java Streams API improve the processing of collections?

Accepted Answer

By enabling parallel processing of elements

Answer

The Java Streams API significantly improves collection processing by enabling parallel execution of operations. By calling `parallelStream()`, developers can easily process elements concurrently across multiple CPU cores, leading to performance gains for large datasets. Streams also promote a functional programming style and do not modify the underlying collection directly.

Question 5

What does the "java.util.concurrent" package primarily provide?

Accepted Answer

Utilities for concurrent programming and synchronization

Answer

The `java.util.concurrent` package is specifically designed to provide a rich set of utilities for concurrent programming in Java. It includes classes for managing threads, thread pools, concurrent data structures (like `ConcurrentHashMap`), and synchronization aids (like `Semaphore` and `CountDownLatch`), making it easier to write robust multi-threaded applications.

(1Z0-811) Oracle Java SE11 Programmer Practice Test

(1Z0-811) Oracle Java SE11 Programmer Practice Test

1Z0-811 Core Java API