Question

1.Write Java code for extending the LinkedList<E> class of java.util.* to ExtLinkedList<E> that would include the following method:

public ExtLinkedList <E> mergeThreeLists (ExtLinkedList<E> list1, ExtLinkedList<E> list2) {

}

that returns an ExtLinkedList<E> which is the merged version of values from this list, followed by values from list1, and then followed by values from list2. For example, if E is Integer type and this list has (5,3,1), list1 has (8, 10,12,14), and list2 has (22,23,24,25,26) in that order, then the returned list from a call to list.mergeThreeLists(list1,list2) will have (5,3,1,8,10,12,14,22,23,24, 25,26). Obviously the size of the returned list will be equal to list.size()+list1.size()+list2.size(). Use listIterator() to do this efficiently for full credit. Your code should work for any size including the empty list and any parameter E.

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. If not, PLEASE let me know before you rate, I’ll help you fix whatever issues. Thanks

//ExtLinkedList.java

import java.util.LinkedList;
import java.util.ListIterator;

public class ExtLinkedList<E> extends LinkedList<E> {

        // required method
        public ExtLinkedList<E> mergeThreeLists(ExtLinkedList<E> list1,
                        ExtLinkedList<E> list2) {
                // if any parameter is null, initializing it to empty list, so that the
                // method works without any issues at all. (note: this would not make
                // any changes to the original parameters passed to the method)
                if (list1 == null) {
                        list1 = new ExtLinkedList<E>();
                }
                if (list2 == null) {
                        list2 = new ExtLinkedList<E>();
                }
                // creating an ExtLinkedList to store result
                ExtLinkedList<E> result = new ExtLinkedList<E>();
                // fetching an iterator from this list
                ListIterator<E> it = this.listIterator();
                // adding each element to result using iterator
                while (it.hasNext()) {
                        result.add(it.next());
                }
                // repeating this for list1
                it = list1.listIterator();
                while (it.hasNext()) {
                        result.add(it.next());
                }
                // repeating this for list2
                it = list2.listIterator();
                while (it.hasNext()) {
                        result.add(it.next());
                }
                // returning final list
                return result;
        }

}