Question

1- Use FirstLastList: Write method public void join(FirstLastList SecondList) such that given two linked lists, join them together to give one. So if the lists lst1= [1,3,7,4] and lst2=[2,4,5,8,6], the result of lst1.join(lst2) is lst1=[1,3,7,4,2,4,5,8,6] and lst2=[].

2- Use FirstLastList: Write method public void swap(). It swaps the first and last elements of a FirstLastList. So if lst1= [1,3,7,4], lst1.swap() = [4,3,7,1]. Display or throw an exception if the list contains less than two elements.

Demonstrate by displaying the list contents before and after calling the above methods. Eg:
lst1
[1,3,7,4]
lst2
[2,4,5,8,6]
lst1.join(lst2)
[1,3,7,4,2,4,5,8,6]

lst1.swap()
[6,3,7,4,2,4,5,8,1]

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// firstLastList.java
// demonstrates list with first and last references
// to run this program: C>java FirstLastApp
////////////////////////////////////////////////////////////////
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 link
private Link last; // ref to last link
// -------------------------------------------------------------
public FirstLastList() // constructor
{
first = null; // no links on list yet
last = null;
}
// -------------------------------------------------------------
public boolean isEmpty() // true if no links
{ return first==null; }
// -------------------------------------------------------------
public void insertFirst(long dd) // insert at front of list
{
Link newLink = new Link(dd); // make new link

if( isEmpty() ) // if empty list,
last = newLink; // newLink <-- last
newLink.next = first; // newLink --> old first
first = newLink; // first --> newLink
}
// -------------------------------------------------------------
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()
{
System.out.print("List (first-->last): ");
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 FirstLastApp
{
public static void main(String[] args)
{ // make a new list
FirstLastList theList = new FirstLastList();

theList.insertFirst(22); // insert at front
theList.insertFirst(44);
theList.insertFirst(66);

theList.insertLast(11); // insert at rear
theList.insertLast(33);
theList.insertLast(55);

theList.displayList(); // display the list

theList.deleteFirst(); // delete first two items
theList.deleteFirst();

theList.displayList(); // display again
} // end main()
} // end class FirstLastApp
////////////////////////////////////////////////////////////////\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\

Class FirstLastAppTest.Java is only for testing. Please do not Edit.

class FirstLastAppTest
{
   public static void main(String[] args)
   {
      FirstLastList lst1 = new FirstLastList();                // Start a new FirstLastList called lst1

      lst1.insertLast(1);                                      // Add links with data to the last position
      lst1.insertLast(3);
      lst1.insertLast(7);
      lst1.insertLast(4);
      System.out.print("\nlst1: ");                               // print the description for the list
      lst1.displayList();                                          // print the contents of the list

      FirstLastList lst2 = new FirstLastList();                // Start a new FirstLastList called lst2

      lst2.insertLast(2);                                      // Add links with data to the last position
      lst2.insertLast(4);
      lst2.insertLast(5);
      lst2.insertLast(8);
      lst2.insertLast(6);
      System.out.print("\nlst2: ");                           // print the description for the list
      lst2.displayList();                                      // print the contents of the list

      System.out.print("\nlst1.join(lst2): ");                // print the action to take place: lst1.join(lst2)
      lst1.join(lst2);                                         // call the join method for lst1 to add lst2
      System.out.print("\nlst1: ");                           // print the description for the list
      lst1.displayList();                                      // print the contents of the list lst1; post join()
      System.out.print("lst2: ");                           // print the description for the list
      lst2.displayList();                                      // print the contents of the list lst2; post join()

      System.out.print("\nlst1.swap(): ");                    // print the action to take place: lst1.swap()
      lst1.swap();                                             // call the swap method for lst1
      System.out.print("\nlst1: ");                           // print the description for the list
      lst1.displayList();                                      // print the contents of the list lst1; post swap()
   }  // end main()
}  // end class 

Answer 1

Save it as FirstLastApp.java

class FirstLastList {

  private Link first; // ref to first link

  private Link last; // ref to last link

  // -------------------------------------------------------------

  public FirstLastList() { // constructor

    first = null; // no links on list yet

    last = null;

  }

  // -------------------------------------------------------------

  public boolean isEmpty() { // true if no links

    return first == null;

  }

  // -------------------------------------------------------------

  public void insertFirst(long dd) { // insert at front of list

    Link newLink = new Link(dd); // make new link

    if (isEmpty()) last = newLink; // if empty list, // newLink <-- last

    newLink.next = first; // newLink --> old first

    first = newLink; // first --> newLink

  }

  // -------------------------------------------------------------

  public void insertLast(long dd) { // insert at end of list

    Link newLink = new Link(dd); // make new link

    if (isEmpty()) first = newLink; // if empty list, // 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) last = null; // if only one item // null <-- last

    first = first.next; // first --> old next

    return temp;

  }

  // -------------------------------------------------------------

  public void displayList() {

    System.out.print("List (first-->last): ");

    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("");

  }

  // -------------------------------------------------------------

  public void join(FirstLastList otherList) {

    Link current = otherList.first; // start at beginning

    while (current != null) { // until end of list,

      this.insertLast(current.dData);

      current = current.next; // move to next link

    }

    otherList.first = null;

  }

  public void swap() throws Exception {

    int count = 0;

    Link current = first; // start at beginning

    while (current != null) { // until end of list,

      count++;

      current = current.next; // move to next link

    }

    if (count < 2) {

      throw new Exception("There is not enough element in the list.");

    } else {

      long firstData = first.dData;

      long lastData = last.dData;

      first.dData = lastData;

      last.dData = firstData;

    }

  }

}

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

////////////////////////////////////////////////////////////////

public class FirstLastApp {

  public static void main(String[] args) { // make a new list

    FirstLastList lst1 = new FirstLastList();

    lst1.insertFirst(1);

    lst1.insertLast(3);

    lst1.insertLast(7);

    lst1.insertLast(4);

    System.out.print("List 1 is : ");

    lst1.displayList();

    FirstLastList lst2 = new FirstLastList();

    lst2.insertFirst(2);

    lst2.insertLast(4);

    lst2.insertLast(5);

    lst2.insertLast(8);

    lst2.insertLast(6);

    System.out.print("\nList 2 is : ");

    lst2.displayList();

    lst1.join(lst2);

    System.out.print("\nAfter joining List 1 is : ");

    lst1.displayList();

    System.out.print("\nList 2 is : ");

    lst2.displayList();

    try {

      lst1.swap();

      System.out.println("\nAfter swap the list 1 is : ");

      lst1.displayList();

      lst2.swap();

      System.out.println("\nAfter swap the list 2 is : ");

      lst2.displayList();

    } catch (Exception e) {

      System.out.println(e);

    }

  }

}

//SAMPLE OUTPUT

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