Question

You must alter the Queue class you created in L5 to make it a CIRCULAR Queue class . Call your class Queue. it must be a template class.

public class Queue <T>{

}

I have put a driver program in the module . It is called CircularQueue.java

This driver program should then run with your Queue class (no modifications allowed to the driver program).

Your Queue class should have at least the following methods: one or more constructors, enqueue, dequeue, peek, isEmpty, getSize, makeEmpty, and printQ.

printQ takes one parameter (an integer) and has return type void. printQ(30) will print 30 elements in the queue. If the queue has fewer than 30 elements (and because it is circular) then you will just keep on going round and round until you have printed out all 30.

Upload your Queue class ONLY to canvas.

Queue Class

import java.util.LinkedList;

public class Queue<T> { //generic class

LinkedList<T> list; // defing linked list: - it implements both list and dequeue interface
// Queue follows first in last out approach

Queue() { //constructor
list = new LinkedList<>(); //inititalizing linkedList
}

void enqueue(T element) { //add element at the last of the list
list.addLast(element);
}

T dequeue() {
if (list.isEmpty() == false) {
return list.pollFirst(); //Retrieves and removes the first element of this list
} else {
System.out.println("List is empty!");
return null;
}
}

int getSize() { // return size of the list
return list.size();
}

void peek() { //Retrieves, but does not remove, the first element of this list.
if (list.isEmpty() == false) {
System.out.println(list.peek());
} else {
System.out.println("List is empty!");
}
}

boolean isEmpty() {
if (list.isEmpty()) {
return true;
} else {
return false;
}
}

void makeEmpty() {
list.removeAll(list);
}

Code must have

constructor

enqueue

dequeue

peek

isEmpty

getSize

makeEmpty

printQ

Answer 1

// Queue.java: Java program to implement a Circular Queue

import java.util.LinkedList;

public class Queue<T> {//generic class

   LinkedList<T> list; // defining linked list: - it implements both list and dequeue interface
   // Queue follows first in last out approach
  
   Queue() { //constructor
       list = new LinkedList<>(); //inititalizing linkedList
   }
  
   void enqueue(T element) { //add element at the last of the list
       list.addLast(element);
   }
  
   T dequeue() {
       if (list.isEmpty() == false) {
           return list.pollFirst(); //Retrieves and removes the first element of this list
       } else {
           System.out.println("List is empty!");
           return null;
       }
   }
  
   int getSize() { // return size of the list
       return list.size();
   }
  
   void peek() { //Retrieves, but does not remove, the first element of this list.
       if (list.isEmpty() == false) {
           System.out.println(list.peek());
       } else {
           System.out.println("List is empty!");
       }
   }
  
   boolean isEmpty() {
       if (list.isEmpty()) {
           return true;
       } else {
           return false;
       }
   }

   void makeEmpty() {
       list.removeAll(list);
   }
  
   /** method that displays the elements of queue, the number of elements displayed is specified by the argument.
   * If the queue has fewer than num_elements then it will just keep on going round and round until num_elements have been displayed
   * @param num_elements, integer specifying the number of elements to display
   */
   void printQ(int num_elements)
   {
       if(isEmpty()) // empty queue
           System.out.println("List is empty!");
       else
       {
           int index = 0; // set index to index of first element i.e 0
          
           // loop num_elements times
           for(int i=0;i<num_elements;i++)
           {
               System.out.print(list.get(index)); // display the element at index
               index++; // increment index by 1
               if(index == getSize()) // end of queue has been reached, reset index to first element i.e 0
                   index = 0;
               if(i < num_elements-1) // this is not the last element, display a comma followed by a space
                   System.out.print(", ");
           }
           System.out.println(); // display a new line at the end
       }
   }

}

// end of Queue.java