Java集合-LinkedList（一）

LinkedList源碼解析

1.成員變量
①size：集合大小
②first：頭結點
③last：尾節點
2.構造器
空構造
帶集合的構造

public LinkedList() {
}
public LinkedList(Collection<? extends E> c) {
    this();
    addAll(c);
}

3.重要內部類

private static class Node<E> {
    E item;//本身元素
    Node<E> next;//前驅，指向該節點的上一個節點，頭結點爲null
    Node<E> prev;//後驅，指向該節點的後一個節點，尾節點爲null

    Node(Node<E> prev, E element, Node<E> next) {
        this.item = element;
        this.next = next;
        this.prev = prev;
    }
}

4主要方法
①添加

//添加頭結點
public void addFirst(E e) {
    linkFirst(e);
}
private void linkFirst(E e) {
    //獲取頭結點
    final Node<E> f = first;
    //生成一個新的頭節點
    final Node<E> newNode = new Node<>(null, e, f);
    //跟新first數據
    first = newNode;
    //如果頭結點爲null，那麼這個節點也是尾節點
    if (f == null)
        last = newNode;
    else
    //否則將原來頭結點的前驅指想新的頭結點
        f.prev = newNode;
    size++;
    modCount++;
}
//添加尾節點
public void addLast(E e) {
    linkLast(e);
}
public boolean add(E e) {
    linkLast(e);
    return true;
}
void linkLast(E e) {
    final Node<E> l = last;
    final Node<E> newNode = new Node<>(l, e, null);
    last = newNode;
    if (l == null)
        first = newNode;
    else
        l.next = newNode;
    size++;
    modCount++;
}
//在指定位置插入節點數據
public void add(int index, E element) {
    //檢查index
    checkPositionIndex(index);

    if (index == size)
        //插入在末尾
        linkLast(element);
    else
        linkBefore(element, node(index));
}
//succ，指定索引位置的節點元素，e要插入的元素數據
void linkBefore(E e, Node<E> succ) {
    // assert succ != null;
    //取得succ的前一個節點
    final Node<E> pred = succ.prev;
    //生成新的節點，前驅指向succ的前驅，後驅指向succ
    final Node<E> newNode = new Node<>(pred, e, succ);
    //succ的前驅指向新節點
    succ.prev = newNode;
    //檢查succ是否爲頭結點
    if (pred == null)
        first = newNode;
    else
    //原來succ的前節點的後驅指向新的節點
        pred.next = newNode;
    size++;
    modCount++;
}
public boolean addAll(Collection<? extends E> c) {
    return addAll(size, c);
}
public boolean addAll(int index, Collection<? extends E> c) {
    //確認索引是否越界
    checkPositionIndex(index);

    Object[] a = c.toArray();
    int numNew = a.length;
    if (numNew == 0)
        return false;

    Node<E> pred, succ;
    if (index == size) {
    //在原集合末尾插入數據
        succ = null;
        pred = last;
    } else {
    //找到插入索引位置的元素，並將他的前驅賦值給pred
        succ = node(index);
        pred = succ.prev;
    }

    for (Object o : a) {
        //循環遍歷a數組
        @SuppressWarnings("unchecked") E e = (E) o;
        //生成新節點，前驅指向pred，後驅爲null
        Node<E> newNode = new Node<>(pred, e, null);
        if (pred == null)
            first = newNode;
        else
        //將pred的後驅指向新節點
            pred.next = newNode;
        //將新加入的節點作爲新的pred
        pred = newNode;
    }
    //如果索引位置爲null，那麼他的前驅爲尾節點
    if (succ == null) {
        last = pred;
    } else {
        //否則，索引位置將succ和他的前驅pred相連
        pred.next = succ;
        succ.prev = pred;
    }

    size += numNew;
    modCount++;
    return true;
}
/**
 * 返回指定索引下的節點
 */
Node<E> node(int index) {
    // assert isElementIndex(index);

    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;
    }
}

②刪除（操作過程和添加類似，不做解釋）

public E remove() {
    return removeFirst();
}
public E removeFirst() {
    final Node<E> f = first;
    if (f == null)
        throw new NoSuchElementException();
    return unlinkFirst(f);
}
private E unlinkFirst(Node<E> f) {

    // assert f == first && f != null;
    final E element = f.item;
    final Node<E> next = f.next;
    f.item = null;
    f.next = null; // help GC
    first = next;
    if (next == null)
        last = null;
    else
        next.prev = null;
    size--;
    modCount++;
    return element;
}
public E removeLast() {
    final Node<E> l = last;
    if (l == null)
        throw new NoSuchElementException();
    return unlinkLast(l);
}
private E unlinkLast(Node<E> l) {
    // assert l == last && l != null;
    final E element = l.item;
    final Node<E> prev = l.prev;
    l.item = null;
    l.prev = null; // help GC
    last = prev;
    if (prev == null)
        first = null;
    else
        prev.next = null;
    size--;
    modCount++;
    return element;
}
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;
}
public E remove(int index) {
    checkElementIndex(index);
    return unlink(node(index));
}
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;
}

③獲取

public E get(int index) {
    checkElementIndex(index);
    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;
}

④包含

    public boolean contains(Object o) {
    return indexOf(o) != -1;
}
//返回對象的下標，沒有返回-1
public int indexOf(Object o) {
    int index = 0;
    if (o == null) {
        for (Node<E> x = first; x != null; x = x.next) {
            if (x.item == null)
                return index;
            index++;
        }
    } else {
        for (Node<E> x = first; x != null; x = x.next) {
            if (o.equals(x.item))
                return index;
            index++;
        }
    }
    return -1;
}

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未完待續