Java Questions & Answers – Data Structures-Queue

This set of Java Multiple Choice Questions & Answers focuses on “Data Structures-Queue”.

1. Which of the below is not a subinterface of Queue?
a) BlockingQueue
b) BlockingEnque
c) TransferQueue
d) BlockingQueue

Explanation: BlockingQueue, TransferQueue and BlockingQueue are subinterfaces of Queue.

2. What is the remaining capacity of BlockingQueue whose intrinsic capacity is not defined?
a) Integer.MAX_VALUE
b) BigDecimal.MAX_VALUE
c) 99999999
d) Integer.INFINITY

Explanation: A BlockingQueue without any intrinsic capacity constraints always reports a remaining capacity of Integer.MAX_VALUE.

a) True
b) False

Explanation: PriorityQueue is not synchronized. BlockingPriorityQueue is the thread safe implementation.

4. What is difference between dequeue() and peek() function of java?
a) dequeue() and peek() remove and return the next time in line
b) dequeue() and peek() return the next item in line
c) dequeue() removes and returns the next item in line while peek() returns the next item in line
d) peek() removes and returns the next item in line while dequeue() returns the next item in line

Explanation: dequeue() removes the item next in line. peek() returns the item without removing it from the queue.

5. What is the difference between Queue and Stack?
a) Stack is LIFO; Queue is FIFO
b) Queue is LIFO; Stack is FIFO
c) Stack and Queue is FIFO
d) Stack and Queue is LIFO

Explanation: Stack is Last in First out (LIFO) and Queue is First in First out(FIFO).
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6. What are the use of front and rear pointers in CircularQueue implementation?
a) Front pointer points to first element; rear pointer points to the last element
b) Rear pointer points to first element; front pointer points to the last element
c) Front and read pointers point to the first element
d) Front pointer points to the first element; rear pointer points to null object

Explanation: CircularQueue implementation is an abstract class where first and rear pointer point to the same object.

7. What is the correct method used to insert and delete items from the queue?
a) push and pop
b) enqueue and dequeue
c) enqueue and peek

Explanation: enqueue is pushing item into queue; dequeue is removing item from queue; peek returns object without removing it from queue.
Stack uses push and pop methods. add and remove are used in the list.

8. Which data structure is used in Breadth First Traversal of a graph?
a) Stack
b) Queue
c) Array
d) Tree

Explanation: In Breadth First Traversal of graph the nodes at the same level are accessed in the order of retrieval (i.e FIFO).

9. Where does a new element be inserted in linked list implementation of a queue?
b) Tail of list
c) At the centre of list
d) All the old entries are pushed and then the new element is inserted

Explanation: To maintain FIFO, newer elements are inserted to the tail of the list.

10. If the size of the array used to implement a circular queue is MAX_SIZE. How rear moves to traverse inorder to insert an element in the queue?
a) rear=(rear%1)+MAX_SIZE
b) rear=(rear+1)%MAX_SIZE
c) rear=rear+(1%MAX_SIZE)
d) rear=rear%(MAX_SIZE+1)

Explanation: The front and rear pointer od circular queue point to the first element.

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