Tag: java

Questions Related to java

Which collection class allows you to grow or shrink its size and provides indexed access to its elements, but whose methods are not synchronized?

java

  1. java.util.HashSet

  2. java.util.LinkedHashSet

  3. java.util.List

  4. java.util.ArrayList

Show answer
Correct Option: D

AI Explanation

To answer this question, you need to understand the characteristics of different collection classes in Java.

Option A) java.util.HashSet - This option is incorrect because HashSet does not provide indexed access to its elements. It does not maintain the order of its elements either.

Option B) java.util.LinkedHashSet - This option is incorrect because LinkedHashSet does not provide indexed access to its elements. It maintains the insertion order of its elements.

Option C) java.util.List - This option is incorrect because List is an interface, not a specific implementation. It can be implemented by various classes such as ArrayList, LinkedList, etc.

Option D) java.util.ArrayList - This option is correct because ArrayList allows you to grow or shrink its size dynamically. It provides indexed access to its elements, meaning you can access elements using their positions in the list. However, the methods of ArrayList are not synchronized, which means they are not thread-safe.

The correct answer is Option D. ArrayList is the collection class that allows you to grow or shrink its size, provides indexed access to its elements, and its methods are not synchronized.

You need to store elements in a collection that guarantees that no duplicates are stored and all elements can be accessed in natural order. Which interface provides that capability?
java

  1. java.util.Map

  2. java.util.Set

  3. java.util.List

  4. java.util.Collection

Show answer
Correct Option: B

Which interface does java.util.Hashtable implement?
java

  1. Java.util.Map

  2. Java.util.List

  3. Java.util.HashTable

  4. Java.util.Collection

Show answer
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?
java

  1. Java.util.Map

  2. Java.util.Set

  3. Java.util.List

  4. Java.util.Collection

Show answer
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?

java

  1. java.util.ArrayList

  2. java.util.LinkedHashMap

  3. java.util.HashMap

  4. java.util.TreeMap

Show answer
Correct Option: B

Which collection class allows you to access its elements by associating a key with an element's value, and provides synchronization?

java

  1. java.util.SortedMap

  2. java.util.TreeMap

  3. java.util.TreeSet

  4. java.util.Hashtable

Show answer
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?

java

  1. float f = 1F;

  2. float f = 1.0;

  3. float f = "1";

  4. float f = 1.0d;

Show answer
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.

What is the numerical range of char?
java

  1. 0 to 32767

  2. 0 to 65535

  3. -256 to 255

  4. -32768 to 32767

Show answer
Correct Option: B

Which is true about an anonymous inner class?
java

  1. It can extend exactly one class and implement exactly one interface.

  2. It can extend exactly one class and can implement multiple interfaces.

  3. It can extend exactly one class or implement exactly one interface.

  4. It can implement multiple interfaces regardless of whether it also extends a class.

Show answer
Correct Option: C
Explanation:

To answer this question, one needs to understand the concept of an anonymous inner class in Java.

An anonymous inner class is a class that is defined and instantiated at the same time, without explicitly giving it a name. It is typically used when you need to create a class that is used only once and does not need to be reused.

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

A. It can extend exactly one class and implement exactly one interface. This option is incorrect. An anonymous inner class can extend a class or implement an interface, but it cannot do both at the same time. It can either extend a class or implement an interface, but not both simultaneously.

B. It can extend exactly one class and can implement multiple interfaces. This option is incorrect. As mentioned earlier, an anonymous inner class cannot extend a class and implement multiple interfaces at the same time. It can either extend a class or implement an interface, but not both simultaneously.

C. It can extend exactly one class or implement exactly one interface. This option is correct. An anonymous inner class can either extend a class or implement an interface. It cannot do both at the same time, but it can choose to extend a class or implement an interface based on the requirements.

D. It can implement multiple interfaces regardless of whether it also extends a class. This option is incorrect. An anonymous inner class can implement multiple interfaces, but only if it does not extend a class. If it extends a class, it can only implement one interface.

Therefore, the correct answer is:

The Answer is: C

Which is true about a method-local inner class?
java

  1. It must be marked final.

  2. It can be marked abstract.

  3. It can be marked public.

  4. It can be marked static.

Show answer
Correct Option: B