USING JAVA ONLY - USING THE CODE BELOW- Write a method public Link last() that c

Question

USING JAVA ONLY - USING THE CODE BELOW-  Write a method public Link last() that could be added to LinkQueue: Return the last data value in the queue; return null if the queue is empty.

USING JAVA ONLY - USING THE CODE BELOW-Write a method public int size() that could be added to LinkQueue: Return the number of elements in the queue.

USING JAVA ONLY - USING THE CODE BELOW- Write a method public void append (LinkQueue queue) that could be in LinkQueue: The executor appends queue's elements in the same order and sets queue to be empty. Precondition: The executor is not empty.

// linkQueue.java
// demonstrates queue implemented as double-ended list
// to run this program: C>java LinkQueueApp
////////////////////////////////////////////////////////////////
class Link
{
public long dData; // data item
public Link next; // next link in list
// -------------------------------------------------------------
public Link(long d) // constructor
{ dData = d; }
// -------------------------------------------------------------
public void displayLink() // display this link
{ System.out.print(dData + " "); }
// -------------------------------------------------------------
} // end class Link
////////////////////////////////////////////////////////////////
class FirstLastList
{
private Link first; // ref to first item
private Link last; // ref to last item
// -------------------------------------------------------------
public FirstLastList() // constructor
{
first = null; // no items on list yet
last = null;
}
// -------------------------------------------------------------
public boolean isEmpty() // true if no links
{ return first==null; }
// -------------------------------------------------------------
public void insertLast(long dd) // insert at end of list
{
Link newLink = new Link(dd); // make new link
if( isEmpty() ) // if empty list,
first = newLink; // first --> newLink
else
last.next = newLink; // old last --> newLink
last = newLink; // newLink <-- last
}
// -------------------------------------------------------------
public long deleteFirst() // delete first link
{ // (assumes non-empty list)
long temp = first.dData;
if(first.next == null) // if only one item
last = null; // null <-- last
first = first.next; // first --> old next
return temp;
}
// -------------------------------------------------------------
public void displayList()
{
Link current = first; // start at beginning
while(current != null) // until end of list,
{
current.displayLink(); // print data
current = current.next; // move to next link
}
System.out.println("");
}
// -------------------------------------------------------------
} // end class FirstLastList
////////////////////////////////////////////////////////////////
class LinkQueue
{
private FirstLastList theList;
//--------------------------------------------------------------
public LinkQueue() // constructor
{ theList = new FirstLastList(); } // make a 2-ended list
//--------------------------------------------------------------
public boolean isEmpty() // true if queue is empty
{ return theList.isEmpty(); }
//--------------------------------------------------------------
public void insert(long j) // insert, rear of queue
{ theList.insertLast(j); }
//--------------------------------------------------------------
public long remove() // remove, front of queue
{ return theList.deleteFirst(); }
//--------------------------------------------------------------
public void displayQueue()
{
System.out.print("Queue (front-->rear): ");
theList.displayList();
}
//--------------------------------------------------------------
} // end class LinkQueue
////////////////////////////////////////////////////////////////
class LinkQueueApp
{
public static void main(String[] args)
{
LinkQueue theQueue = new LinkQueue();
theQueue.insert(20); // insert items
theQueue.insert(40);

theQueue.displayQueue(); // display queue

theQueue.insert(60); // insert items
theQueue.insert(80);

theQueue.displayQueue(); // display queue

theQueue.remove(); // remove items
theQueue.remove();

theQueue.displayQueue(); // display queue
} // end main()
} // end class LinkQueueApp
////////////////////////////////////////////////////////////////

Explanation / Answer

class Link
{
public long dData; // data item
public Link next; // next link in list
// -------------------------------------------------------------
public Link(long d) // constructor
{ dData = d; }
// -------------------------------------------------------------
public void displayLink() // display this link
{ System.out.print(dData + " "); }
// -------------------------------------------------------------
} // end class Link
////////////////////////////////////////////////////////////////
class FirstLastList
{
private Link first; // ref to first item
private Link last; // ref to last item
// -------------------------------------------------------------
public FirstLastList() // constructor
{
first = null; // no items on list yet
last = null;
}
// -------------------------------------------------------------
public boolean isEmpty() // true if no links
{ return first==null; }
// -------------------------------------------------------------
public void insertLast(long dd) // insert at end of list
{
Link newLink = new Link(dd); // make new link
if( isEmpty() ) // if empty list,
first = newLink; // first --> newLink
else
last.next = newLink; // old last --> newLink
last = newLink; // newLink <-- last
}
// -------------------------------------------------------------
public long deleteFirst() // delete first link
{ // (assumes non-empty list)
long temp = first.dData;
if(first.next == null) // if only one item
last = null; // null <-- last
first = first.next; // first --> old next
return temp;
}
// -------------------------------------------------------------
public void displayList()
{
Link current = first; // start at beginning
while(current != null) // until end of list,
{
current.displayLink(); // print data
current = current.next; // move to next link
}
System.out.println("");
}
// -------------------------------------------------------------
} // end class FirstLastList
////////////////////////////////////////////////////////////////
class LinkQueue
{
private FirstLastList theList;
//--------------------------------------------------------------
public LinkQueue() // constructor
{ theList = new FirstLastList(); } // make a 2-ended list
//--------------------------------------------------------------
public boolean isEmpty() // true if queue is empty
{ return theList.isEmpty(); }
//--------------------------------------------------------------
public void insert(long j) // insert, rear of queue
{ theList.insertLast(j); }
//--------------------------------------------------------------
public long remove() // remove, front of queue
{ return theList.deleteFirst(); }
//--------------------------------------------------------------
public void displayQueue()
{
System.out.print("Queue (front-->rear): ");
theList.displayList();

public Liink Last()

{

if(theList.isEmpty())

throw new IllegalStateExceptions("nothing");

else

return theList.Last();

}

public int size()

{

if(theList.isEmpty())

return 0;

else

return next.size();

}

public void append (LinkQueue queue)

{

if(theList.isEmpty())

theList.isEmpty();

else

next.insertInOrder(queue);

}

}
//--------------------------------------------------------------
} // end class LinkQueue
////////////////////////////////////////////////////////////////
class LinkQueueApp
{
public static void main(String[] args)
{
LinkQueue theQueue = new LinkQueue();
theQueue.insert(20); // insert items
theQueue.insert(40);

theQueue.displayQueue(); // display queue

theQueue.insert(60); // insert items
theQueue.insert(80);

theQueue.displayQueue(); // display queue

theQueue.remove(); // remove items
theQueue.remove();

theQueue.displayQueue(); // display queue

theQueue.Last();

int n=theQueue.size();

system.out.println("the size of queue is:"+n);

theQueue.append(queue);
} // end main()
} // end class LinkQueueApp
////////////////////////////////////////////////////////////////

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