public boolean add(E e) {
// 默認添加到尾部,詳見2.1
linkLast(e);
return true;
}
public void addFirst(E e) {
// 添加到頭部 , 詳見2.2
linkFirst(e);
}
public void addLast(E e) {
// 添加到尾部,詳見2.1
linkLast(e);
}
public boolean addAll(Collection<? extends E> c) {
// 添加集合 詳見2.3
return addAll(size, c);
}
2.1尾部添加linkLast(e)
void linkLast(E e) {
// last是成員變量記住鏈表的最後一個node
final Node<E> l = last;
// 初始化Node , pre爲l , next設置爲null(因爲是添加到尾部)
final Node<E> newNode = new Node<>(l, e, null);
last = newNode;
// 如果last == null,說明鏈表是空的
if (l == null)
// 讓該node指向頭部
first = newNode;
else
// 鏈表不是空的,就讓l的next指向新聲明的node
l.next = newNode;
// 長度++
size++;
modCount++;
}
2.2頭部添加linkFirst(e)
private void linkFirst(E e) {
final Node<E> f = first;
final Node<E> newNode = new Node<>(null, e, f);
first = newNode;
// 如果f頭部節點爲null , 說明鏈表是空的
if (f == null)
last = newNode;
else
// 鏈表不是空 設置當前頭部的前一項爲新聲明的node
f.prev = newNode;
size++;
modCount++;
}
2.3 添加集合
public boolean addAll(int index, Collection<? extends E> c) {
checkPositionIndex(index);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
// 聲明兩個node用於存儲臨界數據。pred是待插入鏈表的最前面數據前一項,succ是待插入鏈表的最後一項的後一項
Node<E> pred, succ;
// 如果插在尾部 succ爲null
if (index == size) {
succ = null;
pred = last;
} else {
// 根據index計算前一項,詳見2.4
succ = node(index);
pred = succ.prev;
}
// 遍歷插入的數據
for (Object o : a) {
@SuppressWarnings("unchecked") E e = (E) o;
Node<E> newNode = new Node<>(pred, e, null);
if (pred == null)
first = newNode;
else
pred.next = newNode;
pred = newNode;
}
if (succ == null) {
last = pred;
} else {
pred.next = succ;
succ.prev = pred;
}
size += numNew;
modCount++;
return true;
}
2.4 找到插入前一項
Node<E> node(int index) {
// assert isElementIndex(index);
// 判斷下標與size/2比較,<size/2從0開始遍歷,>size/2從size-1倒序遍歷
if (index < (size >> 1)) {
Node<E> x = first;
for (int i = 0; i < index; i++)
x = x.next;
return x;
} else {
Node<E> x = last;
for (int i = size - 1; i > index; i--)
x = x.prev;
return x;
}
}
3. 刪
public E remove() {
// 默認頭部刪除
return removeFirst();
}
public E remove(int index) {
checkElementIndex(index);
// 刪除節點 詳見3.1
return unlink(node(index));
}
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
// 刪除節點 詳見3.1
return unlinkFirst(f);
}
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
// 刪除節點 詳見3.1
return unlinkLast(l);
}
// 遍歷鏈表unlink操作
public boolean remove(Object o) {
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
3.1 unlink
// unlink比較邏輯簡單
E unlink(Node<E> x) {
// assert x != null;
final E element = x.item;
final Node<E> next = x.next;
final Node<E> prev = x.prev;
if (prev == null) {
first = next;
} else {
prev.next = next;
x.prev = null;
}
if (next == null) {
last = prev;
} else {
next.prev = prev;
x.next = null;
}
x.item = null;
size--;
modCount++;
return element;
}
4. 改
public E set(int index, E element) {
checkElementIndex(index);
// 根據index找到node , node(index)詳見2.4
Node<E> x = node(index);
E oldVal = x.item;
// 替換值
x.item = element;
return oldVal;
}
5. 查
public E get(int index) {
checkElementIndex(index);
// 根據index找到node , node(index)詳見2.4
return node(index).item;
}
public E getFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
public E getLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
public E poll() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}