Java集合类源码分析(四):ArrayList&LinkedList

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Java集合类源码分析(一):Collcetion接口
Java集合类源码分析(二):List接口
Java集合类源码分析(三):AbstractList类
Java集合类源码分析(四):ArrayList&LinkedList
java集合类源码分析(五):Map接口
Java集合类源码分析(六):AbstractMap类
Java集合类源码分析(七):HashMap&LinkedHashMap
Java集合类源码分析(八):AbstractSet类
Java集合类源码分析(九):HashSet&LinkedHashSet

ArrayList源码分析

ArrayList可以放入任何类型的元素
ArrayList不是同步的

/**
 * Default initial capacity.
 */
private static final int DEFAULT_CAPACITY = 10;

/**
 * Shared empty array instance used for empty instances.
 */
private static final Object[] EMPTY_ELEMENTDATA = {};

/**
 * Shared empty array instance used for default sized empty instances. We
 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
 * first element is added.
 */
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

/**
 * The array buffer into which the elements of the ArrayList are stored.
 * The capacity of the ArrayList is the length of this array buffer. Any
 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
 * will be expanded to DEFAULT_CAPACITY when the first element is added.
 */
transient Object[] elementData; // non-private to simplify nested class access

构造函数,如果传入的初始容量大于0,就构造一个数组,否则使用类里本来有的静态空数组

public ArrayList(int initialCapacity) {
    if (initialCapacity > 0) {
        this.elementData = new Object[initialCapacity];
    } else if (initialCapacity == 0) {
        this.elementData = EMPTY_ELEMENTDATA;
    } else {
        throw new IllegalArgumentException("Illegal Capacity: "+
                                           initialCapacity);
    }
}

使用另一个静态空数组

public ArrayList() {
    this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}

构造一个ArrayList,含有集合里的所有元素,顺序与集合迭代器返回的元素顺序相同
如果集合为空,则直接使用静态空数组

public ArrayList(Collection<? extends E> c) {
    elementData = c.toArray();
    if ((size = elementData.length) != 0) {
        // c.toArray might (incorrectly) not return Object[] (see 6260652)
        if (elementData.getClass() != Object[].class)
            elementData = Arrays.copyOf(elementData, size, Object[].class);
    } else {
        // replace with empty array.
        this.elementData = EMPTY_ELEMENTDATA;
    }
}

将列表的容量调整到与元素数量相同,可以用来最小化存储空间

public void trimToSize() {
    modCount++;
    if (size < elementData.length) {
        elementData = (size == 0)
          ? EMPTY_ELEMENTDATA
          : Arrays.copyOf(elementData, size);
    }
}

增大列表容量

public void ensureCapacity(int minCapacity) {
    int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
        // any size if not default element table
        ? 0
        // larger than default for default empty table. It's already
        // supposed to be at default size.
        : DEFAULT_CAPACITY;

    if (minCapacity > minExpand) {
        ensureExplicitCapacity(minCapacity);
    }
}

private void ensureCapacityInternal(int minCapacity) {
    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
        minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
    }

    ensureExplicitCapacity(minCapacity);
}

private void ensureExplicitCapacity(int minCapacity) {
    modCount++;

    // overflow-conscious code
    if (minCapacity - elementData.length > 0)
        grow(minCapacity);
}

将新的容量变为原来容量的1.5倍。

但是需要对扩容后的容量进行检验。共有两种可能

1.得到的容量比需要的容量小,即溢出。

2.得到的容量超过了规定的最大容量,进入hugeCapacity中,如果需要的容量小于0,抛出内存溢出异常,如果需要的容量比规定的最大容量大,那么最大容量只能是 Integer.MAX_VALUE。

最后将elementData 通过Array的复制拷贝方法进行了扩容。

private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

/**
 * Increases the capacity to ensure that it can hold at least the
 * number of elements specified by the minimum capacity argument.
 *
 * @param minCapacity the desired minimum capacity
 */
private void grow(int minCapacity) {
    // overflow-conscious code
    int oldCapacity = elementData.length;
    int newCapacity = oldCapacity + (oldCapacity >> 1);
    if (newCapacity - minCapacity < 0)
        newCapacity = minCapacity;
    if (newCapacity - MAX_ARRAY_SIZE > 0)
        newCapacity = hugeCapacity(minCapacity);
    // minCapacity is usually close to size, so this is a win:
    elementData = Arrays.copyOf(elementData, newCapacity);
}

private static int hugeCapacity(int minCapacity) {
    if (minCapacity < 0) // overflow
        throw new OutOfMemoryError();
    return (minCapacity > MAX_ARRAY_SIZE) ?
        Integer.MAX_VALUE :
        MAX_ARRAY_SIZE;
}

返回一个原列表的浅拷贝,即没有拷贝元素

public Object clone() {
    try {
        ArrayList<?> v = (ArrayList<?>) super.clone();
        v.elementData = Arrays.copyOf(elementData, size);
        v.modCount = 0;
        return v;
    } catch (CloneNotSupportedException e) {
        // this shouldn't happen, since we are Cloneable
        throw new InternalError(e);
    }
}

返回一个含有列表所有元素的数组

public Object[] toArray() {
    return Arrays.copyOf(elementData, size);
}

@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
    if (a.length < size)
        // Make a new array of a's runtime type, but my contents:
        return (T[]) Arrays.copyOf(elementData, size, a.getClass());
    System.arraycopy(elementData, 0, a, 0, size);
    if (a.length > size)
        a[size] = null;
    return a;
}

调用ensureCapacityInternal(size + 1)

public boolean add(E e) {
    ensureCapacityInternal(size + 1);  // Increments modCount!!
    elementData[size++] = e;
    return true;
}

删除列表中第一个与参数元素相同的元素

 public boolean remove(Object o) {
    if (o == null) {
        for (int index = 0; index < size; index++)
            if (elementData[index] == null) {
                fastRemove(index);
                return true;
            }
    } else {
        for (int index = 0; index < size; index++)
            if (o.equals(elementData[index])) {
                fastRemove(index);
                return true;
            }
    }
    return false;
}

用来删除的私有方法,跳过边界检查,也不返回删除的元素

ArrayList对列表的结构性修改,都是调用System.arrayCopy拷贝一部分不变的元素实现的

private void fastRemove(int index) {
    modCount++;
    int numMoved = size - index - 1;
    if (numMoved > 0)
        System.arraycopy(elementData, index+1, elementData, index,
                         numMoved);
    elementData[--size] = null; // clear to let GC do its work
}

根据参数complement决定是保存还是删除列表中与参数列表中相同的元素

首先对集合中的对象数组进行了一次复制,然后将数组中的元素依次与collection进行对比。try{}块的结果就是得到了一个数组,数组前w位元素或与collection相同(complement=true的时候)或不同(complement=false)。

下面来看finally,先来看第二个if{}代码块,它的作用就是把数组中w以后的元素全部变为null值,让gc来回收。

现在回到finally的第一个if中,看条件(r != size),似乎永远不会满足这个条件吧。上面的for循环一直r++啊,可是别忘了,c.contains(elementData[r])这句话是有可能抛出异常的,如果一旦类型不匹配,就会抛出异常 进入finally中。
这个方法,如果没有删除任何数据,那么将会返回false。

public boolean removeAll(Collection<?> c) {
    Objects.requireNonNull(c);
    return batchRemove(c, false);
}

public boolean retainAll(Collection<?> c) {
    Objects.requireNonNull(c);
    return batchRemove(c, true);
}

private boolean batchRemove(Collection<?> c, boolean complement) {
    final Object[] elementData = this.elementData;
    int r = 0, w = 0;
    boolean modified = false;
    try {
        for (; r < size; r++)
            if (c.contains(elementData[r]) == complement)
                elementData[w++] = elementData[r];
    } finally {
        // Preserve behavioral compatibility with AbstractCollection,
        // even if c.contains() throws.
        if (r != size) {
            System.arraycopy(elementData, r,
                             elementData, w,
                             size - r);
            w += size - r;
        }
        if (w != size) {
            // clear to let GC do its work
            for (int i = w; i < size; i++)
                elementData[i] = null;
            modCount += size - w;
            size = w;
            modified = true;
        }
    }
    return modified;
}

将列表写入输出流

private void writeObject(java.io.ObjectOutputStream s)
    throws java.io.IOException{
    // Write out element count, and any hidden stuff
    int expectedModCount = modCount;
    s.defaultWriteObject();

    // Write out size as capacity for behavioural compatibility with clone()
    s.writeInt(size);

    // Write out all elements in the proper order.
    for (int i=0; i<size; i++) {
        s.writeObject(elementData[i]);
    }

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

由输入流获得列表信息

private void readObject(java.io.ObjectInputStream s)
    throws java.io.IOException, ClassNotFoundException {
    elementData = EMPTY_ELEMENTDATA;

    // Read in size, and any hidden stuff
    s.defaultReadObject();

    // Read in capacity
    s.readInt(); // ignored

    if (size > 0) {
        // be like clone(), allocate array based upon size not capacity
        ensureCapacityInternal(size);

        Object[] a = elementData;
        // Read in all elements in the proper order.
        for (int i=0; i<size; i++) {
            a[i] = s.readObject();
        }
    }
}

迭代所有,每个元素都执行Consumer中定义的方法,可能会改变元素的值

@Override
public void forEach(Consumer<? super E> action) {
    Objects.requireNonNull(action);
    final int expectedModCount = modCount;
    @SuppressWarnings("unchecked")
    final E[] elementData = (E[]) this.elementData;
    final int size = this.size;
    for (int i=0; modCount == expectedModCount && i < size; i++) {
        action.accept(elementData[i]);
    }
    if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
    }
}

删除符合过滤器要求的元素

@Override
public boolean removeIf(Predicate<? super E> filter) {
    Objects.requireNonNull(filter);
    // figure out which elements are to be removed
    // any exception thrown from the filter predicate at this stage
    // will leave the collection unmodified
    int removeCount = 0;
    final BitSet removeSet = new BitSet(size);
    final int expectedModCount = modCount;
    final int size = this.size;
    for (int i=0; modCount == expectedModCount && i < size; i++) {
        @SuppressWarnings("unchecked")
        final E element = (E) elementData[i];
        if (filter.test(element)) {
            removeSet.set(i);
            removeCount++;
        }
    }
    if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
    }

    // shift surviving elements left over the spaces left by removed elements
    final boolean anyToRemove = removeCount > 0;
    if (anyToRemove) {
        final int newSize = size - removeCount;
        for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
            i = removeSet.nextClearBit(i);
            elementData[j] = elementData[i];
        }
        for (int k=newSize; k < size; k++) {
            elementData[k] = null;  // Let gc do its work
        }
        this.size = newSize;
        if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();
        }
        modCount++;
    }

    return anyToRemove;
}

替换所有元素,即对所有元素进行operator定义的操作

@Override
@SuppressWarnings("unchecked")
public void replaceAll(UnaryOperator<E> operator) {
    Objects.requireNonNull(operator);
    final int expectedModCount = modCount;
    final int size = this.size;
    for (int i=0; modCount == expectedModCount && i < size; i++) {
        elementData[i] = operator.apply((E) elementData[i]);
    }
    if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
    }
    modCount++;
}

排序

@Override
@SuppressWarnings("unchecked")
public void sort(Comparator<? super E> c) {
    final int expectedModCount = modCount;
    Arrays.sort((E[]) elementData, 0, size, c);
    if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
    }
    modCount++;
}

LinkedList源码分析

双向链表

不是同步的


transient int size = 0;

//指向第一个结点的指针
    /**
     * Pointer to first node.
     * Invariant: (first == null && last == null) ||
     *            (first.prev == null && first.item != null)
     */
    transient Node first;

//指向最后一个结点的指针
    /**
     * Pointer to last node.
     * Invariant: (first == null && last == null) ||
     *            (last.next == null && last.item != null)
     */
    transient Node last;
public LinkedList() {
}

使用集合创建列表,列表含有集合中所有元素,顺序与集合迭代器返回的元素顺序相同

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

将参数元素连接到首位

private void linkFirst(E e) {
    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++;
}

将参数元素连接到最后一位

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++;
}

在第二个参数节点之前插入一个新节点
1. 创建newNode节点,将newNode的后继指针指向succ,前驱指针指向pred
2. 将succ的前驱指针指向newNode
3. 根据pred是否为null,进行不同操作。
– 如果pred为null,说明该节点插入在头节点之前,要重置first头节点
– 如果pred不为null,那么直接将pred的后继指针指向newNode即可

void linkBefore(E e, Node<E> succ) {
    // 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++;
}

解除第一个元素的链接

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;
}

解除最后一个元素的链接

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;
}

删除某个元素的链接

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;
}

返回列表的第一个节点

public E getFirst() {
    final Node<E> f = first;
    if (f == null)
        throw new NoSuchElementException();
    return f.item;
}

返回列表的最后一个节点

public E getLast() {
    final Node<E> l = last;
    if (l == null)
        throw new NoSuchElementException();
    return l.item;
}

删除并返回列表的第一个节点

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

删除并返回列表的最后一个节点

public E removeLast() {
    final Node<E> l = last;
    if (l == null)
        throw new NoSuchElementException();
    return unlinkLast(l);
}

将参数元素连接到首位

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

将参数元素连接到最后一位

public void addLast(E e) {
    linkLast(e);
}

将参数元素连接到列表最后一位,与addLast效果相同

public boolean add(E e) {
    linkLast(e);
    return true;
}

如果列表中含有参数元素,则删除它的第一次出现

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;
}

将集合中的元素全部加入列表中

public boolean addAll(Collection<? extends E> c) {
    return addAll(size, c);
}

在指定位置处,插入集合中的所有元素,顺序与集合迭代器返回元素顺序相同
1. 检查index索引范围
2. 得到集合数据
3. 得到插入位置的前驱和后继节点
4. 遍历数据,将数据插入到指定位置

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;
}
  1. 检查index的范围,否则抛出异常
  2. 如果插入位置是链表尾部,那么调用linkLast方法
  3. 如果插入位置是链表中间,那么调用linkBefore方法

    public void add(int index, E element) {
    checkPositionIndex(index);

    if (index == size)
        linkLast(element);
    else
        linkBefore(element, node(index));
    

    }

返回链表的头部结点

public E peek() {
    final Node<E> f = first;
    return (f == null) ? null : f.item;
}

返回链表的头部结点

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

删除并返回链表的头部结点

public E poll() {
    final Node<E> f = first;
    return (f == null) ? null : unlinkFirst(f);
}

删除并返回链表的头部结点

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

将参数元素连接到链表尾部

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

将参数元素连接到链表头部

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

将参数元素连接到链表尾部

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

返回链表的头部结点

public E peekFirst() {
    final Node<E> f = first;
    return (f == null) ? null : f.item;
 }

返回链表的尾部结点

public E peekLast() {
    final Node<E> l = last;
    return (l == null) ? null : l.item;
}

删除并返回链表的头部结点

public E pollFirst() {
    final Node<E> f = first;
    return (f == null) ? null : unlinkFirst(f);
}

删除并返回链表的头部结点

public E pollLast() {
    final Node<E> l = last;
    return (l == null) ? null : unlinkLast(l);
}

将参数元素连接到链表头部

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

删除并返回链表的头部结点

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

删除参数元素在链表中的第一次出现

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

删除参数元素在链表中的最后一次出现

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;
}

浅拷贝

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;
}
    原文作者:java集合源码分析
    原文地址: https://blog.csdn.net/devil_bye/article/details/80315989
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