(keep it simple please) Problem 2 (List Implementation) (35 points): Suppose that you want an operation for the ADT List that returns the first position of a given object in the list. The header of the method is as follows: public int getFirstPosition(T anObject) where T is the general type of the objects in the list. Write an implementation of this method for the LList class. Include testing of the method in the main method of the LList class. ------------------------------------------------------------- /** An interface for the ADT list. Entries in the list have positions that begin with 1. @author Frank M. Carrano @version 3.0 */ public interface ListInterface { /** Adds a new entry to the end of this list. Entries currently in the list are unaffected. The lists size is increased by 1. @param newEntry the object to be added as a new entry */ public void add(T newEntry); /** Adds a new entry at a specified position within this list. Entries originally at and above the specified position are at the next higher position within the list. The lists size is increased by 1. @param newPosition an integer that specifies the desired position of the new entry @param newEntry the object to be added as a new entry @return true if the addition is successful, or false if newPosition < 1, or newPosition > getLength() + 1 */ public boolean add(int newPosition, T newEntry); /** Removes the entry at a given position from this list. Entries originally at positions higher than the given position are at the next lower position within the list, and the lists size is decreased by 1. @param givenPosition an integer that indicates the position of the entry to be removed @return a reference to the removed entry or null, if either the list was empty, givenPosition < 1, or givenPosition > getLength() */ public T remove(int givenPosition); /** Removes all entries from this list. */ public void clear(); /** Replaces the entry at a given position in this list. @param givenPosition an integer that indicates the position of the entry to be replaced @param newEntry the object that will replace the entry at the position givenPosition @return true if the replacement occurs, or false if either the list is empty, givenPosition < 1, or givenPosition > getLength() */ public boolean replace(int givenPosition, T newEntry); /** Retrieves the entry at a given position in this list. @param givenPosition an integer that indicates the position of the desired entry @return a reference to the indicated entry or null, if either the list is empty, givenPosition < 1, or givenPosition > getLength() */ public T getEntry(int givenPosition); /** Sees whether this list contains a given entry. @param anEntry the object that is the desired entry @return true if the list contains anEntry, or false if not */ public boolean contains(T anEntry); /** Gets the length of this list. @return the integer number of entries currently in the list */ public int getLength(); /** Sees whether this list is empty. @return true if the list is empty, or false if not */ public boolean isEmpty(); /** Retrieves all entries that are in this list in the order in which they occur in the list. */ public T[] toArray(); } // end ListInterface 

 ----------------------------------------------------------------------- import java.io.*; class LList implements ListInterface { private Node firstNode; // reference to first node private int numberOfEntries; public LList() { clear(); } // end default constructor public final void clear() // note the final method { firstNode = null; numberOfEntries = 0; } // end clear public void add(T newEntry) { Node newNode = new Node(newEntry); if (isEmpty()) { firstNode = newNode; } else // add to end of nonempty list { Node lastNode = getNodeAt(numberOfEntries); lastNode.next = newNode; // make last node reference new node } // end if numberOfEntries++; } // end add public boolean add(int newPosition, T newEntry) { boolean isSuccessful = true; if ((newPosition >= 1) && (newPosition <= numberOfEntries + 1)) { Node newNode = new Node(newEntry); if (newPosition == 1) // case 1 { newNode.setNextNode(firstNode); firstNode = newNode; } else // case 2: list is not empty { // and newPosition > 1 Node nodeBefore = getNodeAt(newPosition - 1); Node nodeAfter = nodeBefore.getNextNode(); newNode.setNextNode(nodeAfter); nodeBefore.setNextNode(newNode); } // end if numberOfEntries++; } else { isSuccessful = false; } return isSuccessful; } // end add public T remove(int givenPosition) { T result = null; // return value if ((givenPosition >= 1) && (givenPosition <= numberOfEntries)) { assert !isEmpty(); if (givenPosition == 1) // case 1: remove first entry { result = firstNode.getData(); // save entry to be removed firstNode = firstNode.getNextNode(); } else // case 2: not first entry { Node nodeBefore = getNodeAt(givenPosition - 1); Node nodeToRemove = nodeBefore.getNextNode(); Node nodeAfter = nodeToRemove.getNextNode(); nodeBefore.setNextNode(nodeAfter); result = nodeToRemove.getData(); // save entry to be removed } // end if numberOfEntries--; } // end if return result; // return removed entry, or // null if operation fails } // end remove public boolean contains(T anEntry) { boolean found = false; Node currentNode = firstNode; while (!found && (currentNode != null)) { if (anEntry.equals(currentNode.getData())) { found = true; } else { currentNode = currentNode.getNextNode(); } } // end while return found; } // end contains public T getEntry(int givenPosition) { T result = null; // result to return if ((givenPosition >= 1) && (givenPosition <= numberOfEntries)) { assert !isEmpty(); result = getNodeAt(givenPosition).getData(); } // end if return result; } // end getEntry public boolean replace(int givenPosition, T newEntry) { boolean isSuccessful = true; if ((givenPosition >= 1) && (givenPosition <= numberOfEntries)) { assert !isEmpty(); Node desiredNode = getNodeAt(givenPosition); desiredNode.setData(newEntry); } else { isSuccessful = false; } return isSuccessful; } // end replace public int getLength() { return numberOfEntries; } public boolean isEmpty() { boolean result; if (numberOfEntries == 0) // or getLength() == 0 { assert firstNode == null; result = true; } else { assert firstNode != null; result = false; } // end if return result; } // end isEmpty public T[] toArray() { // the cast is safe because the new array contains null entries @SuppressWarnings("unchecked") T[] result = (T[]) new Object[numberOfEntries]; int index = 0; Node currentNode = firstNode; while ((index < numberOfEntries) && (currentNode != null)) { result[index] = currentNode.getData(); currentNode = currentNode.getNextNode(); index++; } // end while return result; } // end toArray private Node getNodeAt(int givenPosition) { assert (firstNode != null) && (1 <= givenPosition) && (givenPosition <= numberOfEntries); Node currentNode = firstNode; // traverse the chain to locate the desired node for (int counter = 1; counter < givenPosition; counter++) { currentNode = currentNode.getNextNode(); } assert currentNode != null; return currentNode; } // end getNodeAt private class Node { private T data; // entry in bag private Node next; // link to next node private Node(T dataPortion) { this(dataPortion, null); } // end constructor private Node(T dataPortion, Node nextNode) { data = dataPortion; next = nextNode; } // end constructor private T getData() { return data; } // end getData private void setData(T newData) { data = newData; } // end setData private Node getNextNode() { return next; } // end getNextNode private void setNextNode(Node nextNode) { next = nextNode; } // end setNextNode } // end Node /** Build a string representation of the list * * @return a string showing the state of the list */ public String toString() { String result = "{ "; Node currentNode = firstNode; while (currentNode != null) { result = result + "<" + currentNode.data + "> "; currentNode = currentNode.next; } result = result + "}"; return result; } /** Display the list with indices one to a line * This will correctly display an infinite list, * whereas the toString() method will never return * */ public void display() { int index = 1; Node currentNode = firstNode; while (currentNode != null) { System.out.println(index + ":" + currentNode.getData()); currentNode = currentNode.getNextNode(); index++; } } // end display /** Check to see if two lists are the same. * @param aList another linked list to check this list against * @return true if all the items in this list and the other list are equals */ public boolean equals(LList aList) { boolean isEqual = false; // result of comparison of lists Node currOne = firstNode; Node currTwo = aList.firstNode; int counter; if (numberOfEntries == aList.numberOfEntries) { // lists have equal lengths, so traverse both and compare items as you go: // (NOTE: loop is skipped if lists are empty) while ((currOne != null) && (currOne.getData()).equals(currTwo.getData())) { currOne = currOne.getNextNode(); currTwo = currTwo.getNextNode(); } // end while isEqual = currOne == null; } else // lists have unequal lengths { isEqual = false; } return isEqual; } // end equals } }