Write the method addLast(). public class DoubleEndedQueue implements Queue { private class Node { private T data; private Node next; public Node(T item) { data = item; next = null; } } private Node head; private Node tail; private int size; public DoubleEndedQueue() { head = null; tail = null; size = 0; } public void addLast(T item) { // to be implemented } public T removeFirst() { if (size == 0) { return null; } T removed = head.data; head = head.next; if (size == 1) { tail = head; } size--; return removed; } public T getFirst() { if (size == 0) { return null; } return head.data; } public boolean contains (T item) { Node current = head; while (current!= null) { if (item.equals(current.data)) { return true; } current = current.next; } return false; } public int size() { return size; } public String toString() { String s = "["; Node current = head; while (current != null) { s += current.data; if (current.next != null) { s += ", "; } current = current.next; } return s + "]"; } public Iterator iterator() { return new LinkedIterator(); } private void checkForNull(T item) { if (item == null) { throw new IllegalArgumentException("null not a possible value!"); } } private class LinkedIterator implements Iterator { private Node position; public LinkedIterator() { position = head; } public boolean hasNext() { return position!= null; } public T next() { if (hasNext()) { T item = position.data; position = position.next; return item; } else { throw new NoSuchElementException ("Off end of list"); } } public void remove() { throw new UnsupportedOperationException(); } } }

Write the method addLast(). public class DoubleEndedQueue implements Queue { private class Node { private T data; private Node next; public Node(T item) { data = item; next = null; } } private Node head; private Node tail; private int size; public DoubleEndedQueue() { head = null; tail = null; size = 0; } public void addLast(T item) { // to be implemented } public T removeFirst() { if (size == 0) { return null; } T removed = head.data; head = head.next; if (size == 1) { tail = head; } size--; return removed; } public T getFirst() { if (size == 0) { return null; } return head.data; } public boolean contains (T item) { Node current = head; while (current!= null) { if (item.equals(current.data)) { return true; } current = current.next; } return false; } public int size() { return size; } public String toString() { String s = "["; Node current = head; while (current != null) { s += current.data; if (current.next != null) { s += ", "; } current = current.next; } return s + "]"; } public Iterator iterator() { return new LinkedIterator(); } private void checkForNull(T item) { if (item == null) { throw new IllegalArgumentException("null not a possible value!"); } } private class LinkedIterator implements Iterator { private Node position; public LinkedIterator() { position = head; } public boolean hasNext() { return position!= null; } public T next() { if (hasNext()) { T item = position.data; position = position.next; return item; } else { throw new NoSuchElementException ("Off end of list"); } } public void remove() { throw new UnsupportedOperationException(); } } }

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Related questions

Question

Write the method addLast().

public class DoubleEndedQueue<T> implements Queue<T>
{
   private class Node
   {
       private T data;
       private Node next;

       public Node(T item)
       {
           data = item;
           next = null;
       }
   }

   private Node head;
   private Node tail;
   private int size;

   public DoubleEndedQueue()
   {
       head = null;
       tail = null;
       size = 0;
   }

   public void addLast(T item)
   {
       // to be implemented
   }

   public T removeFirst()
   {
       if (size == 0)
       {
           return null;
       }

T removed = head.data;
head = head.next;

       if (size == 1)
       {
           tail = head;
       }

       size--;
       return removed;
   }

   public T getFirst()
   {
       if (size == 0)
       {
           return null;
       }

return head.data;
}

   public boolean contains (T item)
   {
       Node current = head;

       while (current!= null)
       {
           if (item.equals(current.data))
           {
               return true;
           }

current = current.next;
}

return false;
}

   public int size()
   {
       return size;
   }

   public String toString()
   {
       String s = "[";
       Node current = head;

       while (current != null)
       {
           s += current.data;

           if (current.next != null)
           {
               s += ", ";
           }

current = current.next;
}

return s + "]";
}

   public Iterator<T> iterator()
   {
       return new LinkedIterator();
   }

   private void checkForNull(T item)
   {
       if (item == null)
       {
           throw new IllegalArgumentException("null not a possible value!");
       }
   }

   private class LinkedIterator implements Iterator<T>
   {
       private Node position;

       public LinkedIterator()
       {
           position = head;
       }

       public boolean hasNext()
       {
           return position!= null;
       }

       public T next()
       {
           if (hasNext())
           {
               T item = position.data;
               position = position.next;
               return item;
           }

           else
           {
               throw new NoSuchElementException ("Off end of list");
           }
       }

       public void remove()
       {
           throw new UnsupportedOperationException();
       }
   }
}

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