public LinkedList() 
{
             
        header.next = header.previous = header;
}

Constructs an empty list.

 public LinkedList(Collection c) 
{
        this();
        addAll(c);
}

Constructs a list containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Parameters:

c - the collection whose elements are to be placed into this list

Throws:

NullPointerException - if the specified collection is null

 public boolean add(E e) 
{
        addBefore(e, header);
        return true;
}

Appends the specified element to the end of this list.

This method is equivalent to #addLast .

 public  void add(int index,
    E element) 
{
        addBefore(element, (index==size ? header : entry(index)));
}

Inserts the specified element at the specified position in this list. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).

 public boolean addAll(Collection c) 
{
        return addAll(size, c);
}

Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's iterator. The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (Note that this will occur if the specified collection is this list, and it's nonempty.)

 public boolean addAll(int index,
    Collection c) 
{
        if (index <  0 || index  > size)
            throw new IndexOutOfBoundsException("Index: "+index+
                                                ", Size: "+size);
        Object[] a = c.toArray();
        int numNew = a.length;
        if (numNew==0)
            return false;
        modCount++;
        Entry< E > successor = (index==size ? header : entry(index));
        Entry< E > predecessor = successor.previous;
        for (int i=0; i< numNew; i++) {
            Entry< E > e = new Entry< E >((E)a[i], successor, predecessor);
            predecessor.next = e;
            predecessor = e;
        }
        successor.previous = predecessor;
        size += numNew;
        return true;
}

Inserts all of the elements in the specified collection into this list, starting at the specified position. Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices). The new elements will appear in the list in the order that they are returned by the specified collection's iterator.

 public  void addFirst(E e) 
{
        addBefore(e, header.next);
}

Inserts the specified element at the beginning of this list.

 public  void addLast(E e) 
{
        addBefore(e, header);
}

Appends the specified element to the end of this list.

This method is equivalent to #add .

 public  void clear() 
{
        Entry< E > e = header.next;
        while (e != header) {
            Entry< E > next = e.next;
            e.next = e.previous = null;
            e.element = null;
            e = next;
        }
        header.next = header.previous = header;
        size = 0;
        modCount++;
}

Removes all of the elements from this list.

 public Object clone() 
{
        LinkedList< E > clone = null;
        try {
            clone = (LinkedList< E >) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }
        // Put clone into "virgin" state
        clone.header = new Entry< E >(null, null, null);
        clone.header.next = clone.header.previous = clone.header;
        clone.size = 0;
        clone.modCount = 0;
        // Initialize clone with our elements
        for (Entry< E > e = header.next; e != header; e = e.next)
            clone.add(e.element);
        return clone;
}

Returns a shallow copy of this LinkedList. (The elements themselves are not cloned.)

 public boolean contains(Object o) 
{
        return indexOf(o) != -1;
}

Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).

 public Iterator descendingIterator() 
{
        return new DescendingIterator();
}

 public E element() 
{
        return getFirst();
}

Retrieves, but does not remove, the head (first element) of this list.

 public E get(int index) 
{
        return entry(index).element;
}

Returns the element at the specified position in this list.

 public E getFirst() 
{
        if (size==0)
            throw new NoSuchElementException();
        return header.next.element;
}

Returns the first element in this list.

 public E getLast() 
{
        if (size==0)
            throw new NoSuchElementException();
        return header.previous.element;
}

Returns the last element in this list.

 public int indexOf(Object o) 
{
        int index = 0;
        if (o==null) {
            for (Entry e = header.next; e != header; e = e.next) {
                if (e.element==null)
                    return index;
                index++;
            }
        } else {
            for (Entry e = header.next; e != header; e = e.next) {
                if (o.equals(e.element))
                    return index;
                index++;
            }
        }
        return -1;
}

Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.

 public int lastIndexOf(Object o) 
{
        int index = size;
        if (o==null) {
            for (Entry e = header.previous; e != header; e = e.previous) {
                index--;
                if (e.element==null)
                    return index;
            }
        } else {
            for (Entry e = header.previous; e != header; e = e.previous) {
                index--;
                if (o.equals(e.element))
                    return index;
            }
        }
        return -1;
}

Returns the index of the last occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the highest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.

 public ListIterator listIterator(int index) 
{
        return new ListItr(index);
}

Returns a list-iterator of the elements in this list (in proper sequence), starting at the specified position in the list. Obeys the general contract of List.listIterator(int).

The list-iterator is fail-fast: if the list is structurally modified at any time after the Iterator is created, in any way except through the list-iterator's own remove or add methods, the list-iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

 public boolean offer(E e) 
{
        return add(e);
}

Adds the specified element as the tail (last element) of this list.

 public boolean offerFirst(E e) 
{
        addFirst(e);
        return true;
}

Inserts the specified element at the front of this list.

 public boolean offerLast(E e) 
{
        addLast(e);
        return true;
}

Inserts the specified element at the end of this list.

 public E peek() 
{
        if (size==0)
            return null;
        return getFirst();
}

Retrieves, but does not remove, the head (first element) of this list.

 public E peekFirst() 
{
        if (size==0)
            return null;
        return getFirst();
}

Retrieves, but does not remove, the first element of this list, or returns null if this list is empty.

 public E peekLast() 
{
        if (size==0)
            return null;
        return getLast();
}

Retrieves, but does not remove, the last element of this list, or returns null if this list is empty.

 public E poll() 
{
        if (size==0)
            return null;
        return removeFirst();
}

Retrieves and removes the head (first element) of this list

 public E pollFirst() 
{
        if (size==0)
            return null;
        return removeFirst();
}

Retrieves and removes the first element of this list, or returns null if this list is empty.

 public E pollLast() 
{
        if (size==0)
            return null;
        return removeLast();
}

Retrieves and removes the last element of this list, or returns null if this list is empty.

 public E pop() 
{
        return removeFirst();
}

Pops an element from the stack represented by this list. In other words, removes and returns the first element of this list.

This method is equivalent to #removeFirst() .

 public  void push(E e) 
{
        addFirst(e);
}

Pushes an element onto the stack represented by this list. In other words, inserts the element at the front of this list.

This method is equivalent to #addFirst .

 public E remove() 
{
        return removeFirst();
}

Retrieves and removes the head (first element) of this list.

 public boolean remove(Object o) 
{
        if (o==null) {
            for (Entry< E > e = header.next; e != header; e = e.next) {
                if (e.element==null) {
                    remove(e);
                    return true;
                }
            }
        } else {
            for (Entry< E > e = header.next; e != header; e = e.next) {
                if (o.equals(e.element)) {
                    remove(e);
                    return true;
                }
            }
        }
        return false;
}

Removes the first occurrence of the specified element from this list, if it is present. If this list does not contain the element, it is unchanged. More formally, removes the element with the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))) (if such an element exists). Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call).

 public E remove(int index) 
{
        return remove(entry(index));
}

Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices). Returns the element that was removed from the list.

 public E removeFirst() 
{
        return remove(header.next);
}

Removes and returns the first element from this list.

 public boolean removeFirstOccurrence(Object o) 
{
        return remove(o);
}

Removes the first occurrence of the specified element in this list (when traversing the list from head to tail). If the list does not contain the element, it is unchanged.

 public E removeLast() 
{
        return remove(header.previous);
}

Removes and returns the last element from this list.

 public boolean removeLastOccurrence(Object o) 
{
        if (o==null) {
            for (Entry< E > e = header.previous; e != header; e = e.previous) {
                if (e.element==null) {
                    remove(e);
                    return true;
                }
            }
        } else {
            for (Entry< E > e = header.previous; e != header; e = e.previous) {
                if (o.equals(e.element)) {
                    remove(e);
                    return true;
                }
            }
        }
        return false;
}

Removes the last occurrence of the specified element in this list (when traversing the list from head to tail). If the list does not contain the element, it is unchanged.

 public E set(int index,
    E element) 
{
        Entry< E > e = entry(index);
        E oldVal = e.element;
        e.element = element;
        return oldVal;
}

Replaces the element at the specified position in this list with the specified element.

 public int size() 
{
        return size;
}

Returns the number of elements in this list.

 public Object[] toArray() 
{
        Object[] result = new Object[size];
        int i = 0;
        for (Entry< E > e = header.next; e != header; e = e.next)
            result[i++] = e.element;
        return result;
}

Returns an array containing all of the elements in this list in proper sequence (from first to last element).

The returned array will be "safe" in that no references to it are maintained by this list. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

 public T[] toArray(T[] a) 
{
        if (a.length <  size)
            a = (T[])java.lang.reflect.Array.newInstance(
                                a.getClass().getComponentType(), size);
        int i = 0;
        Object[] result = a;
        for (Entry< E > e = header.next; e != header; e = e.next)
            result[i++] = e.element;
        if (a.length  > size)
            a[size] = null;
        return a;
}

Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the list fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this list.

If the list fits in the specified array with room to spare (i.e., the array has more elements than the list), the element in the array immediately following the end of the list is set to null. (This is useful in determining the length of the list only if the caller knows that the list does not contain any null elements.)

Like the #toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a list known to contain only strings. The following code can be used to dump the list into a newly allocated array of String:

String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function to toArray().