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Java Objects and Collections Quiz

Description: Java Objects and Collections Quiz
Number of Questions: 10
Created by:
Tags: java
Attempted 0/10 Correct 0 Score 0
  1. TreeMap

  2. HashMap

  3. LinkedHashMap

  4. The answer depends on the implementation of the existing instance.


Correct Option: C
Explanation:

To solve this question, the user needs to know the differences between the concrete implementations of the Map interface and their iteration orders.

Now, let's go through each option and explain why it is right or wrong:

A. TreeMap: This option is incorrect because TreeMap sorts its elements in natural order or by a custom Comparator, whereas the iteration order of the existing instance of the Map may not be sorted. Thus, creating a new instance of TreeMap would not preserve the same iteration order as the existing instance.

B. HashMap: This option is incorrect because HashMap does not guarantee any particular iteration order. Thus, creating a new instance of HashMap would not preserve the same iteration order as the existing instance.

C. LinkedHashMap: This option is correct. LinkedHashMap is similar to HashMap but maintains a doubly-linked list running through all its entries, which allows it to maintain the insertion order. Thus, creating a new instance of LinkedHashMap would preserve the same iteration order as the existing instance.

D. The answer depends on the implementation of the existing instance: This option is incorrect because the iteration order of the existing instance of the Map may not be guaranteed by all implementations of the Map interface. Thus, it is not a reliable solution to assume that any implementation of the Map interface would preserve the same iteration order as the existing instance.

The Answer is: C. LinkedHashMap

Which class does not override the equals() and hashCode() methods, inheriting them directly from class Object?

  1. java.lang.String

  2. java.lang.Double

  3. java.lang.StringBuffer

  4. java.lang.Character


Correct Option: C
  1. Java.util.Map

  2. Java.util.List

  3. Java.util.HashTable

  4. Java.util.Collection


Correct Option: A
Explanation:

Hash table based implementation of the Map interface.

Which interface provides the capability to store objects using a key-value pair?

  1. Java.util.Map

  2. Java.util.Set

  3. Java.util.List

  4. Java.util.Collection


Correct Option: A
Explanation:

An object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most one value.

Which collection class allows you to associate its elements with key values, and allows you to retrieve objects in FIFO (first-in, first-out) sequence?

  1. java.util.ArrayList

  2. java.util.LinkedHashMap

  3. java.util.HashMap

  4. java.util.TreeMap


Correct Option: B
  1. java.util.SortedMap

  2. java.util.TreeMap

  3. java.util.TreeSet

  4. java.util.Hashtable


Correct Option: D
Explanation:

To solve this question, the user needs to have a basic understanding of Java collections and their functionalities. Specifically, they need to be familiar with the concept of accessing elements by associating a key with a value and the concept of synchronization in Java collections.

Now, let's go through each option and explain why it is right or wrong:

A. java.util.SortedMap: This option is incorrect. While a SortedMap allows you to access its elements by associating a key with an element's value, it does not provide synchronization. To ensure thread-safe access to a SortedMap, you would need to use additional synchronization mechanisms such as the Collections.synchronizedSortedMap() method.

B. java.util.TreeMap: This option is incorrect. Although a TreeMap allows you to access its elements by associating a key with an element's value, it does not inherently provide synchronization. To achieve synchronized access to a TreeMap, you would need to use additional synchronization mechanisms such as the Collections.synchronizedSortedMap() method.

C. java.util.TreeSet: This option is incorrect. A TreeSet is not a collection class that allows you to access elements by associating a key with an element's value. It is an implementation of the Set interface that stores elements in a sorted and unique order.

D. java.util.Hashtable: This option is correct. Hashtable is a collection class in Java that allows you to access its elements by associating a key with an element's value. It also provides synchronization, meaning that multiple threads can safely access and modify the Hashtable concurrently without causing data inconsistency or other concurrency issues.

Therefore, the correct answer is:

The Answer is: D. java.util.Hashtable

Which is valid declaration of a float?

  1. float f = 1F;

  2. float f = 1.0;

  3. float f = "1";

  4. float f = 1.0d;


Correct Option: A

AI Explanation

To answer this question, we need to understand the valid ways to declare a float.

Option A) float f = 1F; - This option is correct because it uses the "F" suffix to indicate that the number is a float literal. In Java, the default type for floating-point numbers is double, so adding the "F" suffix is necessary to explicitly declare the variable as a float.

Option B) float f = 1.0; - This option is incorrect because the literal value 1.0 is considered a double by default. To assign a double value to a float variable, you need to explicitly cast it by adding the "F" suffix, like in Option A.

Option C) float f = "1"; - This option is incorrect because it tries to assign a string literal to a float variable. In Java, you cannot directly assign a string to a float without first converting it using appropriate methods.

Option D) float f = 1.0d; - This option is incorrect because the "d" suffix indicates that the literal value is a double. As mentioned earlier, to assign a double value to a float variable, you need to explicitly cast it by adding the "F" suffix.

The correct answer is A) float f = 1F; because it correctly declares a float variable by using the "F" suffix to indicate a float literal.

  1. 0 to 32767

  2. 0 to 65535

  3. -256 to 255

  4. -32768 to 32767


Correct Option: B
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