Need Help Add code for the methods addBoxcarToFront and removeBoxcarFromFront. Do not change the tests or methods. Should complete all tests. Thank you

Using JUnit version 4.12 and hamcrest-core-1.3.

public class SingleLinkList { private Boxcar head; private int size; public SingleLinkList() { head = null; size = 0; } public String toString() { String s = "engine"; if (head != null) { Boxcar boxcar = head; do { s = s + "->" + boxcar.data().toString(); boxcar = boxcar.next(); } while (boxcar != null); } return s; } public int size() { return size; } public void addBoxcarToEnd(Boxcar b) { if (head == null) head = b; else { // Find the last boxcar and add it to the end Boxcar boxcar = head; while (boxcar.next() != null) boxcar = boxcar.next();

boxcar.setNext(b); } size++; } public void addBoxcarToFront(Boxcar b) { } public void removeBoxcarFromFront() { } public void removeBoxcarFromEnd() { if (head != null) { // If there is just one boxcar remove it if (head.next() == null) head = null; else { // Find the last boxcar and remove it Boxcar boxcar = head; Boxcar prevBoxcar = head; while (boxcar.next() != null) { prevBoxcar = boxcar; boxcar = boxcar.next(); } prevBoxcar.setNext(null); } size--; } } }

TEST

import static org.junit.Assert.*;

import org.junit.After;

import org.junit.Before;

import org.junit.Test;

public class SingleLinkListTest

{

@Test public void testAddOneToFront() { SingleLinkList sll = new SingleLinkList(); Boxcar bc1 = new Boxcar("first"); sll.addBoxcarToFront(bc1); assertEquals("engine->first", sll.toString()); assertEquals(1, sll.size()); }

@Test public void testAddTwoToFront() { SingleLinkList sll = new SingleLinkList(); Boxcar bc1 = new Boxcar("first"); Boxcar bc2 = new Boxcar("second"); sll.addBoxcarToFront(bc1); sll.addBoxcarToFront(bc2); assertEquals("engine->second->first", sll.toString()); assertEquals(2, sll.size()); }

@Test public void testAddFifteenToFront() { SingleLinkList sll = new SingleLinkList(); for (int i = 1; i < 16; i++) { Boxcar bc = new Boxcar(i + ""); sll.addBoxcarToFront(bc); } assertEquals("engine->15->14->13->12->11->10->9->8->7->6->5->4->3->2->1", sll.toString()); assertEquals(15, sll.size()); }

@Test public void testAddOneToEnd() { SingleLinkList sll = new SingleLinkList(); Boxcar bc1 = new Boxcar("first"); sll.addBoxcarToEnd(bc1); assertEquals("engine->first", sll.toString()); assertEquals(1, sll.size()); } @Test public void testAddTwoToEnd() { SingleLinkList sll = new SingleLinkList(); Boxcar bc1 = new Boxcar("first"); Boxcar bc2 = new Boxcar("second"); sll.addBoxcarToEnd(bc1); sll.addBoxcarToEnd(bc2); assertEquals("engine->first->second", sll.toString()); assertEquals(2, sll.size()); } @Test public void testAddFifteenToEnd() { SingleLinkList sll = new SingleLinkList(); for (int i = 1; i < 16; i++) { Boxcar bc = new Boxcar(i + ""); sll.addBoxcarToEnd(bc); } assertEquals("engine->1->2->3->4->5->6->7->8->9->10->11->12->13->14->15", sll.toString()); assertEquals(15, sll.size());

@Test public void testRemoveFromFront() { SingleLinkList sll = new SingleLinkList(); Boxcar bc1 = new Boxcar("first"); Boxcar bc2 = new Boxcar("second"); sll.addBoxcarToFront(bc1); sll.addBoxcarToEnd(bc2); assertEquals("engine->first->second", sll.toString()); assertEquals(2, sll.size()); sll.removeBoxcarFromFront(); assertEquals("engine->second", sll.toString()); assertEquals(1, sll.size()); sll.removeBoxcarFromFront(); assertEquals("engine", sll.toString()); assertEquals(0, sll.size()); } @Test public void testRemoveFromEnd() { SingleLinkList sll = new SingleLinkList(); Boxcar bc1 = new Boxcar("first"); Boxcar bc2 = new Boxcar("second"); sll.addBoxcarToFront(bc1); sll.addBoxcarToEnd(bc2); assertEquals("engine->first->second", sll.toString()); assertEquals(2, sll.size()); sll.removeBoxcarFromEnd(); assertEquals("engine->first", sll.toString()); assertEquals(1, sll.size()); sll.removeBoxcarFromEnd(); assertEquals("engine", sll.toString()); assertEquals(0, sll.size()); } @Test public void testAssortedAddsRemoves() { SingleLinkList sll = new SingleLinkList(); Boxcar bc1 = new Boxcar("first"); Boxcar bc2 = new Boxcar("second"); Boxcar bc3 = new Boxcar("third"); sll.addBoxcarToFront(bc1); sll.addBoxcarToEnd(bc2); sll.addBoxcarToEnd(bc3); assertEquals("engine->first->second->third", sll.toString()); assertEquals(3, sll.size()); sll.removeBoxcarFromEnd(); sll.addBoxcarToFront(bc3); assertEquals("engine->third->first->second", sll.toString()); assertEquals(3, sll.size()); sll.removeBoxcarFromEnd(); sll.addBoxcarToFront(bc2); assertEquals("engine->second->third->first", sll.toString()); assertEquals(3, sll.size()); sll.removeBoxcarFromEnd(); sll.addBoxcarToFront(bc1); assertEquals("engine->first->second->third", sll.toString()); assertEquals(3, sll.size()); sll.removeBoxcarFromEnd(); assertEquals("engine->first->second", sll.toString()); assertEquals(2, sll.size()); sll.removeBoxcarFromFront(); assertEquals("engine->second", sll.toString()); assertEquals(1, sll.size()); sll.removeBoxcarFromEnd(); assertEquals("engine", sll.toString()); assertEquals(0, sll.size()); } @Test public void testRemoveFromEnds() { SingleLinkList sll = new SingleLinkList(); for (int i = 1; i < 16; i++) { Boxcar bc = new Boxcar(i + ""); sll.addBoxcarToFront(bc); } assertEquals("engine->15->14->13->12->11->10->9->8->7->6->5->4->3->2->1", sll.toString()); assertEquals(15, sll.size()); sll.removeBoxcarFromFront(); sll.removeBoxcarFromEnd(); assertEquals("engine->14->13->12->11->10->9->8->7->6->5->4->3->2", sll.toString()); assertEquals(13, sll.size()); sll.removeBoxcarFromFront(); sll.removeBoxcarFromEnd(); sll.removeBoxcarFromFront(); assertEquals("engine->12->11->10->9->8->7->6->5->4->3", sll.toString()); assertEquals(10, sll.size()); sll.removeBoxcarFromEnd(); sll.removeBoxcarFromFront(); sll.removeBoxcarFromEnd(); sll.removeBoxcarFromFront(); sll.removeBoxcarFromEnd(); assertEquals("engine->10->9->8->7->6", sll.toString()); assertEquals(5, sll.size()); for (int i = 0; i < 5; i++) sll.removeBoxcarFromEnd(); assertEquals("engine", sll.toString()); assertEquals(0, sll.size()); } }

BOXCAR

public class Boxcar {

// instance variables

private String data;

private Boxcar next;

//Constructor for objects of class Boxcar

public Boxcar(String s)

{

// initialise instance variables

data = s;

next = null;

}

public void setNext(Boxcar n)

{

next = n;

}

public Boxcar next()

{

return next;

}

public void setData(String s)

{

data = s;

}

public String data()

{

return data

}

}