Tag: java

Questions Related to java

  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.

  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

  1. float f = 1F;

  2. float f = 1.0;

  3. float f = "1";

  4. float f = 1.0d;


Correct Option: A
  1. 0 to 32767

  2. 0 to 65535

  3. -256 to 255

  4. -32768 to 32767


Correct Option: B

Which is true about an anonymous inner class?

  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.


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?

  1. It must be marked final.

  2. It can be marked abstract.

  3. It can be marked public.

  4. It can be marked static.


Correct Option: B

AI Explanation

To answer this question, let's go through each option to understand why it is correct or incorrect:

Option A) It must be marked final - This option is incorrect. Method-local inner classes do not have any restrictions on being marked as final. They can be marked as final, but it is not a requirement.

Option B) It can be marked abstract - This option is correct. Method-local inner classes can be marked as abstract. This allows the class to have abstract methods that must be implemented by any non-abstract subclasses.

Option C) It can be marked public - This option is incorrect. Method-local inner classes cannot be marked as public. They can only have either default (package-private) or private access modifiers.

Option D) It can be marked static - This option is incorrect. Method-local inner classes cannot be marked as static. They are implicitly associated with an instance of the enclosing class and cannot exist without an instance of the enclosing class.

Therefore, the correct answer is B) It can be marked abstract. This option is correct because method-local inner classes can be marked as abstract and have abstract methods.

Please select the most appropriate option.