Can someone help me to fix the code please? package dlist; import java.util.Iterator; public class DList implements Iterable<String> { private static class DListNode { public String data; public DListNode next; public DListNode previous; } private DListNode nil; private int size; public DList() { nil = new DListNode(); nil.previous = nil; nil.next = nil; nil.data = null; size = 0; } public void addFirst(String elem) { DListNode newNode = new DListNode(); newNode.data = elem; newNode.next = nil.next; newNode.previous = nil; nil.next.previous = newNode; nil.next = newNode; size++; } public void addLast(String elem) { DListNode newNode = new DListNode(); newNode.data = elem; newNode.next = nil; newNode.previous = nil.previous; nil.previous.next = newNode; nil.previous = newNode; size++; } public String getFirst() { if (size == 0) { throw new RuntimeException("DList is empty"); } return nil.next.data; } public String getLast() { if (size == 0) { throw new RuntimeException("DList is empty"); } return nil.previous.data; } public String removeFirst() { if (size == 0) { throw new RuntimeException("DList is empty"); } DListNode first = nil.next; first.next.previous = nil; nil.next = first.next; size--; return first.data; } public String removeLast() { if (size == 0) { throw new RuntimeException("DList is empty"); } DListNode last = nil.previous; last.previous.next = nil; nil.previous = last.previous; size--; return last.data; } public String get(int index) { if (index < 0 || index >= size) { throw new IndexOutOfBoundsException(); } DListNode node = nil.next; for (int i = 0; i < index; i++) { node = node.next; } return node.data; } public String set(int index, String value) { if (index < 0 || index >= size) { throw new IndexOutOfBoundsException(); } DListNode node = nil.next; for (int i = 0; i < index; i++) { node = node.next; } String oldValue = node.data; node.data = value; return oldValue; } public boolean contains(Object obj) { DListNode node = nil.next; while (node != nil) { if (node.data.equals(obj)) { return true; } node = node.next; } return false; } public int size() { return size; } public int indexOf(Object obj) { int index = 0; DListNode node = nil.next; while (node != nil) { if (node.data.equals(obj)) { return index; } index++; node = node.next; } return -1; } @Override public Iterator<String> iterator() { return new DListIterator(); } private class DListIterator implements Iterator<String> { private DListNode pointer; public DListIterator() { if(nil.next==nil) { pointer = nil; } else pointer=nil.next; } public boolean hasNext() { return pointer != nil; } } }.

1. Can someone help me to fix the code please?
package dlist;
import java.util.Iterator;
public class DList implements Iterable<String> {
private static class DListNode {
public String data;
public DListNode next;
public DListNode previous;
}
private DListNode nil;
private int size;
public DList() {
nil = new DListNode();
nil.previous = nil;
nil.next = nil;
nil.data = null;
size = 0;
}
public void addFirst(String elem) {
DListNode newNode = new DListNode();
newNode.data = elem;
newNode.next = nil.next;
newNode.previous = nil;
nil.next.previous = newNode;
nil.next = newNode;
size++;
}
public void addLast(String elem) {
DListNode newNode = new DListNode();
newNode.data = elem;
newNode.next = nil;
newNode.previous = nil.previous;
nil.previous.next = newNode;
nil.previous = newNode;
size++;
}
public String getFirst() {
if (size == 0) {
throw new RuntimeException("DList is empty");
}
return nil.next.data;
}

2. public String getLast() {
if (size == 0) {
throw new RuntimeException("DList is empty");
}
return nil.previous.data;
}
public String removeFirst() {
if (size == 0) {
throw new RuntimeException("DList is empty");
}
DListNode first = nil.next;
first.next.previous = nil;
nil.next = first.next;
size--;
return first.data;
}
public String removeLast() {
if (size == 0) {
throw new RuntimeException("DList is empty");
}
DListNode last = nil.previous;
last.previous.next = nil;
nil.previous = last.previous;
size--;
return last.data;
}
public String get(int index) {
if (index < 0 || index >= size) {
throw new IndexOutOfBoundsException();
}
DListNode node = nil.next;
for (int i = 0; i < index; i++) {
node = node.next;
}
return node.data;
}
public String set(int index, String value) {
if (index < 0 || index >= size) {
throw new IndexOutOfBoundsException();
}
DListNode node = nil.next;
for (int i = 0; i < index; i++) {

3. node = node.next;
}
String oldValue = node.data;
node.data = value;
return oldValue;
}
public boolean contains(Object obj) {
DListNode node = nil.next;
while (node != nil) {
if (node.data.equals(obj)) {
return true;
}
node = node.next;
}
return false;
}
public int size() {
return size;
}
public int indexOf(Object obj)
{
int index = 0;
DListNode node = nil.next;
while (node != nil)
{
if (node.data.equals(obj))
{
return index;
}
index++;
node = node.next;
}
return -1;
}
@Override
public Iterator<String> iterator()
{
return new DListIterator();
}
private class DListIterator implements Iterator<String>
{
private DListNode pointer;

4. public DListIterator()
{
if(nil.next==nil)
{
pointer = nil;
}
else
pointer=nil.next;
}
public boolean hasNext()
{
return pointer != nil;
}
}
}