Explication détaillée de LinkedList dans les collections Java

LinkedList est une liste doublement chaînée qui hérite de AbstractSequentialList. Elle peut également être utilisée comme une pile, une file d'attente ou une file d'attente à double extrémité.

LinkedList implémente l'interface List et peut y effectuer des opérations de file d'attente.

LinkedList implémente l'interface Seque et peut utiliser LinkedList comme file d'attente à double extrémité.

LinkedList implémente Cloneable, couvrant la fonction clone et peut être cloné.

LinkedList implémente Serialisable et peut être sérialisé.

LinkedList n'est pas thread-safe.

Exemple de programme LinkedList :

public class Hello {

    public static void main(String[] args) {
        testLinkedListAPIs() ;
        useLinkedListAsLIFO();
        useLinkedListAsFIFO();
    }

    private static void testLinkedListAPIs()
    {
        String val = null;
        LinkedList llist = new LinkedList();
        //添加是哪个元素
        llist.add("1");
        llist.add("2");
        llist.add("3");
        llist.add(1, "4");//在第一个元素后面插入4
        System.out.println("\nTest \"addFirst(), removeFirst(), getFirst()\"");
        llist.addFirst("10");//将10插入并作为第一个元素
        System.out.println("llist:"+llist);
        System.out.println("llist.removeFirst():"+llist.removeFirst());//删除掉第一个元素
        System.out.println("llist:"+llist);
        System.out.println("llist.getFirst():"+llist.getFirst());//获得第一个元素
        System.out.println("\nTest \"offerFirst(), pollFirst(), peekFirst()\"");
        llist.offerFirst("10");//添加第一个元素
        System.out.println("llist:"+llist);
        System.out.println("llist.pollFirst():"+llist.pollFirst());//去掉第一个元素
        System.out.println("llist:"+llist);
        System.out.println("llist.peekFirst():"+llist.peekFirst());//读取第一个元素
        System.out.println("\nTest \"addLast(), removeLast(), getLast()\"");
        llist.addLast("20");//链尾添加元素20
        System.out.println("llist:"+llist);
        System.out.println("llist.removeLast():"+llist.removeLast());//删掉链尾元素20
        System.out.println("llist:"+llist);
        System.out.println("llist.getLast():"+llist.getLast());//读取链尾元素
        System.out.println("\nTest \"offerLast(), pollLast(), peekLast()\"");
        llist.offerLast("20");//添加链尾元素20
        System.out.println("llist:"+llist);
        System.out.println("llist.pollLast():"+llist.pollLast());//删掉链尾元素20
        System.out.println("llist:"+llist);
        System.out.println("llist.peekLast():"+llist.peekLast());//读取链尾元素
        llist.set(2, "300");//替换第三个元素
        System.out.println("\nget(3):"+llist.get(2));//获得第三个元素

        String[] arr = (String[])llist.toArray(new String[0]);//得到数组
        for (String str:arr)
        {
            System.out.println("str:"+str);
            System.out.println("size:"+llist.size());
            llist.clear();
            System.out.println("isEmpty():"+llist.isEmpty()+"\n");
        }
    }
    private static void useLinkedListAsLIFO()
    {
        System.out.println("\nuseLinkedListAsLIFO");
        LinkedList stack = new LinkedList();
        //类似于栈输入
        stack.push("1");
        stack.push("2");
        stack.push("3");
        stack.push("4");
        System.out.println("stack:"+stack);
        System.out.println("stack.pop():"+stack.pop());//出栈
        System.out.println("stack.peek():"+stack.peek());//只输出栈顶元素并不出栈
        System.out.println("stack:"+stack);
    }

    private static void useLinkedListAsFIFO()
    {
        System.out.println("\nuseLinkedListAsFIFO");
        LinkedList queue = new LinkedList();
        //类似于队列，入队
        queue.add("10");
        queue.add("20");
        queue.add("30");
        queue.add("40");
        System.out.println("queue:"+queue);
        System.out.println("queue.remove():"+queue.remove());//队列出队
        System.out.println("queue.element():"+queue.element());//读取队头，并不删除元素
        System.out.println("queue:"+queue);
    }
}

Résultat de sortie :

Test "offerLast(), pollLast(), peekLast()"
llist:[1, 4, 2, 3, 20]
llist.pollLast():20
llist:[1, 4, 2, 3]
llist.peekLast():3
get(3):300
str:1
size:4
isEmpty():true
str:4
size:0
isEmpty():true
str:300
size:0
isEmpty():true
str:3
size:0
isEmpty():true
useLinkedListAsLIFO
stack:[4, 3, 2, 1]
stack.pop():4
stack.peek():3
stack:[3, 2, 1]
useLinkedListAsFIFO
queue:[10, 20, 30, 40]
queue.remove():10
queue.element():20
queue:[20, 30, 40]

Code source de LinkedList :

public class LinkedList<E> extends AbstractSequentialList<E>
        implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{
    transient int size = 0; //其实大小为0
    transient Node<E> first; //第一个节点
    transient Node<E> last; //最后一个节点
    public LinkedList() {    //构造一个空LinkedList
    }
    public LinkedList(Collection<? extends E> c) { //构造一个带有输入集合的
        this();
        addAll(c);
    }
    private void linkFirst(E e) { //链接第一个节点
        final Node<E> f = first;
        final Node<E> newNode = new Node<>(null, e, f);
        first = newNode;
        if (f == null)
            last = newNode;
        else
            f.prev = newNode;
        size++;
        modCount++;
    }
    void linkLast(E e) { //链接最后一个节点
        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++;
    }
    void linkBefore(E e, Node<E> succ) { //在节点succ前插入一个e
        // assert succ != null;
        final Node<E> pred = succ.prev;
        final Node<E> newNode = new Node<>(pred, e, succ);
        succ.prev = newNode;
        if (pred == null)
            first = newNode;
        else
            pred.next = newNode;
        size++;
        modCount++;
    }
    //不再链接第一个非空的节点
    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;
    }
    //删掉最后一个节点
    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;
    }
    //删掉节点X
    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;
    }
    //获得第一个节点
    public E getFirst() {
        final Node<E> f = first;
        if (f == null)
            throw new NoSuchElementException();
        return f.item;
    }
    //获得最后一个节点
    public E getLast() {
        final Node<E> l = last;
        if (l == null)
            throw new NoSuchElementException();
        return l.item;
    }
    //删除第一个节点
    public E removeFirst() {
        final Node<E> f = first;
        if (f == null)
            throw new NoSuchElementException();
        return unlinkFirst(f);
    }
    //删除最后一个节点
    public E removeLast() {
        final Node<E> l = last;
        if (l == null)
            throw new NoSuchElementException();
        return unlinkLast(l);
    }
    //在头节点插入E
    public void addFirst(E e) {
        linkFirst(e);
    }
    //在尾节点插入E
    public void addLast(E e) {
        linkLast(e);
    }
    //是否包含某个对象
    public boolean contains(Object o) {
        return indexOf(o) != -1;
    }
    //链表长度
    public int size() {
        return size;
    }
    //在链表中添加节点
    public boolean add(E e) {
        linkLast(e);
        return true;
    }
    //删掉某个节点
    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;
    }
    //在链表尾追加集合
    public boolean addAll(Collection<? extends E> c) {
        return addAll(size, c);
    }
    //在某个节点之后追加集合
    public boolean addAll(int index, Collection<? extends E> c) {
        checkPositionIndex(index);

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

        Node<E> pred, succ;
        if (index == size) {
            succ = null;
            pred = last;
        } else {
            succ = node(index);
            pred = succ.prev;
        }

        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;
    }
    //清空链表
    public void clear() {
        for (Node<E> x = first; x != null; ) {
            Node<E> next = x.next;
            x.item = null;
            x.next = null;
            x.prev = null;
            x = next;
        }
        first = last = null;
        size = 0;
        modCount++;
    }
    //获得第几个节点
    public E get(int index) {
        checkElementIndex(index);
        return node(index).item;
    }
    //对某个节点修改
    public E set(int index, E element) {
        checkElementIndex(index);
        Node<E> x = node(index);
        E oldVal = x.item;
        x.item = element;
        return oldVal;
    }
    //在index节点之前插入一个节点element
    public void add(int index, E element) {
        checkPositionIndex(index);

        if (index == size)
            linkLast(element);
        else
            linkBefore(element, node(index));
    }
    //删除掉下标为index的节点
    public E remove(int index) {
        checkElementIndex(index);
        return unlink(node(index));
    }
    //测试此index下是否有节点
    private boolean isElementIndex(int index) {
        return index >= 0 && index < size;
    }
    //下标位置在链表内
    private boolean isPositionIndex(int index) {
        return index >= 0 && index <= size;
    }
    //下标越界
    private String outOfBoundsMsg(int index) {
        return "Index: "+index+", Size: "+size;
    }
    //检查下标下的节点
    private void checkElementIndex(int index) {
        if (!isElementIndex(index))
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
    //判断下标位置
    private void checkPositionIndex(int index) {
        if (!isPositionIndex(index))
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
    //返回下标节点
    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;
        }
    }
    //查找是否存在节点并返回下标，不存在返回-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;
    }
    //返回最后一个相同的节点的下标
    public int lastIndexOf(Object o) {
        int index = size;
        if (o == null) {
            for (Node<E> x = last; x != null; x = x.prev) {
                index--;
                if (x.item == null)
                    return index;
            }
        } else {
            for (Node<E> x = last; x != null; x = x.prev) {
                index--;
                if (o.equals(x.item))
                    return index;
            }
        }
        return -1;
    }
    //返回表头数据并不删除
    public E peek() {
        final Node<E> f = first;
        return (f == null) ? null : f.item;
    }
    //返回表头数据
    public E element() {
        return getFirst();
    }
    //获得表头数据，并删除表头
    public E poll() {
        final Node<E> f = first;
        return (f == null) ? null : unlinkFirst(f);
    }
    //删除表头
    public E remove() {
        return removeFirst();
    }
    //在表尾添加数据
    public boolean offer(E e) {
        return add(e);
    }
    //在表头添加数据
    public boolean offerFirst(E e) {
        addFirst(e);
        return true;
    }
    //在表尾添加数据
    public boolean offerLast(E e) {
        addLast(e);
        return true;
    }
    //获得第一个数据，并不删除
    public E peekFirst() {
        final Node<E> f = first;
        return (f == null) ? null : f.item;
    }
    //获得最后一个数据，并不删除
    public E peekLast() {
        final Node<E> l = last;
        return (l == null) ? null : l.item;
    }
    //获得第一个节点并删除
    public E pollFirst() {
        final Node<E> f = first;
        return (f == null) ? null : unlinkFirst(f);
    }
    //获得最后一个节点并删除
    public E pollLast() {
        final Node<E> l = last;
        return (l == null) ? null : unlinkLast(l);
    }
    //入栈
    public void push(E e) {
        addFirst(e);
    }
    //出栈
    public E pop() {
        return removeFirst();
    }
    //删除第一次出现的对象
    public boolean removeFirstOccurrence(Object o) {
        return remove(o);
    }
    //删除最后一次出现的对象
    public boolean removeLastOccurrence(Object o) {
        if (o == null) {
            for (Node<E> x = last; x != null; x = x.prev) {
                if (x.item == null) {
                    unlink(x);
                    return true;
                }
            }
        } else {
            for (Node<E> x = last; x != null; x = x.prev) {
                if (o.equals(x.item)) {
                    unlink(x);
                    return true;
                }
            }
        }
        return false;
    }
    //迭代器
    public ListIterator<E> listIterator(int index) {
        checkPositionIndex(index);
        return new ListItr(index);
    }

    private class ListItr implements ListIterator<E> {
        private Node<E> lastReturned;
        private Node<E> next;
        private int nextIndex;
        private int expectedModCount = modCount;

        ListItr(int index) {
// assert isPositionIndex(index);
            next = (index == size) ? null : node(index);
            nextIndex = index;
        }

        public boolean hasNext() {
            return nextIndex < size;
        }

        public E next() {
            checkForComodification();
            if (!hasNext())
                throw new NoSuchElementException();

            lastReturned = next;
            next = next.next;
            nextIndex++;
            return lastReturned.item;
        }

        public boolean hasPrevious() {
            return nextIndex > 0;
        }

        public E previous() {
            checkForComodification();
            if (!hasPrevious())
                throw new NoSuchElementException();

            lastReturned = next = (next == null) ? last : next.prev;
            nextIndex--;
            return lastReturned.item;
        }

        public int nextIndex() {
            return nextIndex;
        }

        public int previousIndex() {
            return nextIndex - 1;
        }

        public void remove() {
            checkForComodification();
            if (lastReturned == null)
                throw new IllegalStateException();

            Node<E> lastNext = lastReturned.next;
            unlink(lastReturned);
            if (next == lastReturned)
                next = lastNext;
            else
                nextIndex--;
            lastReturned = null;
            expectedModCount++;
        }

        public void set(E e) {
            if (lastReturned == null)
                throw new IllegalStateException();
            checkForComodification();
            lastReturned.item = e;
        }

        public void add(E e) {
            checkForComodification();
            lastReturned = null;
            if (next == null)
                linkLast(e);
            else
                linkBefore(e, next);
            nextIndex++;
            expectedModCount++;
        }

        public void forEachRemaining(Consumer<? super E> action) {
            Objects.requireNonNull(action);
            while (modCount == expectedModCount && nextIndex < size) {
                action.accept(next.item);
                lastReturned = next;
                next = next.next;
                nextIndex++;
            }
            checkForComodification();
        }

        final void checkForComodification() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }
    }

    private static class Node<E> {
        E item;
        Node<E> next;
        Node<E> prev;

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

    /**
     * @since 1.6
     */
    public Iterator<E> descendingIterator() {
        return new DescendingIterator();
    }

    /**
     * Adapter to provide descending iterators via ListItr.previous
     */
    private class DescendingIterator implements Iterator<E> {
        private final ListItr itr = new ListItr(size());
        public boolean hasNext() {
            return itr.hasPrevious();
        }
        public E next() {
            return itr.previous();
        }
        public void remove() {
            itr.remove();
        }
    }

    @SuppressWarnings("unchecked")
    private LinkedList<E> superClone() {
        try {
            return (LinkedList<E>) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new InternalError(e);
        }
    }
    public Object clone() {
        LinkedList<E> clone = superClone();

// Put clone into "virgin" state
        clone.first = clone.last = null;
        clone.size = 0;
        clone.modCount = 0;

// Initialize clone with our elements
        for (Node<E> x = first; x != null; x = x.next)
            clone.add(x.item);

        return clone;
    }
    //生成对象数组
    public Object[] toArray() {
        Object[] result = new Object[size];
        int i = 0;
        for (Node<E> x = first; x != null; x = x.next)
            result[i++] = x.item;
        return result;
    }
    //泛型数组
    @SuppressWarnings("unchecked")
    public <T> 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 (Node<E> x = first; x != null; x = x.next)
            result[i++] = x.item;

        if (a.length > size)
            a[size] = null;

        return a;
    }

    private static final long serialVersionUID = 876323262645176354L;
    //序列化写对象
    private void writeObject(java.io.ObjectOutputStream s)
            throws java.io.IOException {
// Write out any hidden serialization magic
        s.defaultWriteObject();

// Write out size
        s.writeInt(size);

// Write out all elements in the proper order.
        for (Node<E> x = first; x != null; x = x.next)
            s.writeObject(x.item);
    }
    //序列化读对象
    @SuppressWarnings("unchecked")
    private void readObject(java.io.ObjectInputStream s)
            throws java.io.IOException, ClassNotFoundException {
// Read in any hidden serialization magic
        s.defaultReadObject();

// Read in size
        int size = s.readInt();

// Read in all elements in the proper order.
        for (int i = 0; i < size; i++)
            linkLast((E)s.readObject());
    }
    @Override
    public Spliterator<E> spliterator() {
        return new LLSpliterator<E>(this, -1, 0);
    }

    /** A customized variant of Spliterators.IteratorSpliterator */
    static final class LLSpliterator<E> implements Spliterator<E> {
        static final int BATCH_UNIT = 1 << 10;  // batch array size increment
        static final int MAX_BATCH = 1 << 25;  // max batch array size;
        final LinkedList<E> list; // null OK unless traversed
        Node<E> current;      // current node; null until initialized
        int est;              // size estimate; -1 until first needed
        int expectedModCount; // initialized when est set
        int batch;            // batch size for splits

        LLSpliterator(LinkedList<E> list, int est, int expectedModCount) {
            this.list = list;
            this.est = est;
            this.expectedModCount = expectedModCount;
        }

        final int getEst() {
            int s; // force initialization
            final LinkedList<E> lst;
            if ((s = est) < 0) {
                if ((lst = list) == null)
                    s = est = 0;
                else {
                    expectedModCount = lst.modCount;
                    current = lst.first;
                    s = est = lst.size;
                }
            }
            return s;
        }

        public long estimateSize() { return (long) getEst(); }

        public Spliterator<E> trySplit() {
            Node<E> p;
            int s = getEst();
            if (s > 1 && (p = current) != null) {
                int n = batch + BATCH_UNIT;
                if (n > s)
                    n = s;
                if (n > MAX_BATCH)
                    n = MAX_BATCH;
                Object[] a = new Object[n];
                int j = 0;
                do { a[j++] = p.item; } while ((p = p.next) != null && j < n);
                current = p;
                batch = j;
                est = s - j;
                return Spliterators.spliterator(a, 0, j, Spliterator.ORDERED);
            }
            return null;
        }

        public void forEachRemaining(Consumer<? super E> action) {
            Node<E> p; int n;
            if (action == null) throw new NullPointerException();
            if ((n = getEst()) > 0 && (p = current) != null) {
                current = null;
                est = 0;
                do {
                    E e = p.item;
                    p = p.next;
                    action.accept(e);
                } while (p != null && --n > 0);
            }
            if (list.modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }

        public boolean tryAdvance(Consumer<? super E> action) {
            Node<E> p;
            if (action == null) throw new NullPointerException();
            if (getEst() > 0 && (p = current) != null) {
                --est;
                E e = p.item;
                current = p.next;
                action.accept(e);
                if (list.modCount != expectedModCount)
                    throw new ConcurrentModificationException();
                return true;
            }
            return false;
        }

        public int characteristics() {
            return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
        }
    }

}

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