1Z0-819 Core APIs & Data Manipulation

Question 1

Which Java package is primarily used for collections?

Accepted Answer

java.util

Answer

The `java.util` package is the primary location for Java's Collections Framework, which includes interfaces and classes for storing and manipulating groups of objects. This package contains essential data structures like `List`, `Set`, `Map`, `ArrayList`, `HashMap`, and `HashSet`, among many others. It also provides utility classes for various common programming tasks.

Question 2

What does the List interface provide?

Accepted Answer

Ordered collection that allows duplicates

Answer

The `List` interface in Java represents an ordered collection of elements, meaning elements are stored and accessed by their integer index. Unlike `Set`s, `List`s explicitly allow duplicate elements. Implementations like `ArrayList` and `LinkedList` maintain the insertion order of elements.

Question 3

How does the HashMap store data?

Accepted Answer

Using key-value pairs

Answer

A `HashMap` in Java stores data as a collection of key-value pairs. Each key is unique and maps to a specific value. It uses a hashing mechanism to efficiently store and retrieve these pairs, providing fast average-case performance for operations like `put` and `get`.

Question 4

What is the function of the Stream API?

Accepted Answer

To process collections with functional-style operations

Answer

The Java Stream API, introduced in Java 8, provides a powerful and declarative way to process sequences of elements, such as collections or arrays. It enables functional-style operations like filtering, mapping, and reducing data, often in a parallelizable manner. Streams do not store data themselves but rather operate on data sources to produce a result.

Question 5

Which method is used to add an element to a List?

Accepted Answer

add()

Answer

The standard method used to add an element to a `List` in Java is `add()`. This method appends the specified element to the end of the list. There are also overloaded versions of `add()` that allow inserting an element at a specific index.

(1Z0-819) Oracle Java SE 11 Developer Practice Test

(1Z0-819) Oracle Java SE 11 Developer Practice Test

1Z0-819 Core APIs & Data Manipulation