ArrayList源码分析

本文主要是介绍ArrayList源码分析，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

ArrayList

一、成员变量

1、private static final long serialVersionUID = 8683452581122892189L;

serialVersionUID的唯一值判定其为同一个对象。

2、private static final int DEFAULT_CAPACITY = 10;

默认的容量大小

3、private static final Object[] EMPTY_ELEMENTDATA = {};

定义一个空数组，在无参构造中使用

4、private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

默认容量空元素数据

5、transient Object[] elementData; // non-private to simplify nested class access非私有以简化嵌套类访问

为啥要用transient修饰elementData使其不被序列化

elementData是一个缓存数组，它通常会预留一些容量，等容量不足时再扩充容量。假如现在实际有了5个元素，而elementData的大小可能是10，那么在序列化时只需要储存5个元素，数组中的最后五个元素是没有实际意义的，不需要储存。所以ArrayList的设计者将elementData设计为transient，然后在writeObject方法中手动将其序列化，并且只序列化了实际存储的那些元素，而不是整个数组

6、private int size;

定义数组大小

7、protected transient int modCount = 0;

用来计数

二、主方法

有参构造,如果输入的容量initialCapacity大于0，那么elementData数组的大小就等于initialCapacity，如果等于0，那他就是一个空数组，如果小于0，这抛出异常

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);
    }
}

无参构造，elementData等于默认容量空元素数据

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

有参构造，
- elementData = c.toArray(); 先把传入的集合转化为数组在赋值给elementData
- size = elementData.length) != 0 现在数组长度size赋值在判断数组的长度是否等于0
- elementData.getClass() != Object[].class 判断类型是否相同，因为不同的类通过toArray方法返回的不一定是Object类型（如下），这样会导致在调用ArrayList增加Object元素的方法的时候出现错误。
- 如果为true的话及调用Arrays.copyOf方法来实现把类型变为Object。
- 如果size==0，则elementData是空数组

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;
    }
}

这里有一个知识点：.class 用于类而 get Class()用于对象。.class和get Class()使用java程序可以得到运行时的类，其实得到就是 Class 一个泛型的 Class对象 T就是你所调用对象的运行时的类的类型。

class Father{
public void showName()
{
 System.out.println("Father...");
}
}
class Child extends Father{
public void showName()
{
 System.out.println("children");
}
}

Father father = new Child();

System.out.println(Father.class); 结果是 Father

System.out.println(father.getClass()); 结果是Child

Class主要用于反射机制。

将集合的的容量修剪为列表当前大小，可以使用此操作来最小化集合的存储

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

增加此ArrayList实例的容量，如果必要时，确保它至少可以容纳元素的数量由最小容量参数指定。

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);
    }
}

返回数组的长度

public int size() {
    return size;
}

判断数组是否为空

public boolean isEmpty() {
    return size == 0;
}

通过indexof方法判断判断数组是否包含某个值

public boolean contains(Object o) {
    return indexOf(o) >= 0;
}

查找该值在数组中的位置（下标）
- 当o为null时，则对数组进行循环判断，当找到null值时返回下标
- 当o不为null是，用循环找出o的值，并返回下标

public int indexOf(Object o) {
    if (o == null) {
        for (int i = 0; i < size; i++)
            if (elementData[i]==null)
                return i;
    } else {
        for (int i = 0; i < size; i++)
            if (o.equals(elementData[i]))
                return i;
    }
    return -1;
}

和indexof同理，不过这个方式是从数组末尾开始找

public int lastIndexOf(Object o) {
    if (o == null) {
        for (int i = size-1; i >= 0; i--)
            if (elementData[i]==null)
                return i;
    } else {
        for (int i = size-1; i >= 0; i--)
            if (o.equals(elementData[i]))
                return i;
    }
    return -1;
}

这个是ArrayList集合克隆的方法，利用Object类中的Native 本地方法clone()新建一个对象出来把这个对象强转成ArrayList，再把被克隆的集合的elementData和size传入Arrays.copyof拷贝一个elementData数组赋值给新建出来集合的elementData，最后返回这个新建的对象。
- super.clone()，调用Object类中的Native 本地方法

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);
    }
}

- 这个其实就是把elementData数组和size传入Array.copyof拷贝一个elementData数组返回。

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

这个根据传入的数组对象的类型拷贝一个新的数组，也是利用的Arrays.copyof方法。

    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;
    }

根据传入的数组下标获取相应的数组下标的数据，这个修饰不是public公开的。

E elementData(int index) {
    return (E) elementData[index];
}

根据传入的数组下标获取对象的数组数据，首先判断下标是否越界，会判断是否大于size或者小于0如果满足其中一条就抛出下标越界异常，否则就根据下标获取对应的数组数据。

public E get(int index) {
    rangeCheck(index);

    return elementData(index);
}

根据传入的数组下标和数据替换数组中该下标的数据，首先判断下标是否越界，会判断是否大于size或者小于0如果满足其中一条就抛出下标越界异常，接着把该下标的数据取出来返回出去，最后再把传入的数据放到这个数组下标中。

public E set(int index, E element) {
    rangeCheck(index);

    E oldValue = elementData(index);
    elementData[index] = element;
    return oldValue;//返回的是被替换掉的值
}

首先会把size+1作为参数取计算容量是否足够，如果足够就不重新计算容量不足够就会重新计算容量拷贝一个新的数组，最后把这个参数数据添加到size下标，也就是把数据保存到数组最后的一个位置，新增完后把size++。

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

这个方法与上面那个add(e)方法有点不一样这个是根据参数下标再这个下标新增一个数据，首先判断下标是否越界，然后再把size+1去计算容量是否需要扩容，再调用System.arraycopy把参数下标index之后的所有数据都右移，最后把空出来的index这个下标位置填入参数element数据，再把size++。

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

    ensureCapacityInternal(size + 1);  // Increments modCount!!
    System.arraycopy(elementData, index, elementData, index + 1,
                     size - index);
    elementData[index] = element;
    size++;
}

移除指定下标的数据，检查参数下标是否越界，把记录修改次数的modCount++,把该下标的数据取出来用于最后返回，计算需要移动的数据，然后调用System.copyof()方法把这个下标的之后的数据左移，移动完成后把数组最后一个数据设置为null,最后返回这个下标移动之前的数据。

public E remove(int index) {
    rangeCheck(index);

    modCount++;
    E oldValue = elementData(index);

    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

    return oldValue;
}

根据传入的对象数据移除集合中的这个数据，首先判断是对象是否为null循环判断数组是否有null的数据如果有就把这个数组的下标传入fastRemove()方法中做移除的操作,其次使用equals方法循环判断与数组中的数据是否相等如果相等就把数组中这个数据的下标传入fastRemove()方法中做移除的操作，如果以上两种判断都不满足就返回false,否则返回true。

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;
}

用于清空数组，modCount++用于计数，用for循环把每个下标的值置位null，并让size为0，以做到清空数组的操作

public void clear() {
    modCount++;

    // clear to let GC do its work
    for (int i = 0; i < size; i++)
        elementData[i] = null;

    size = 0;
}

在集合后面添加一个集合对象，首先把参数集合对象变成数据对象，然后把这个数组对象的长度+size去计算容量是否需要扩容，最后把参数集合数组对象和elementData传入system.copy()方法拷贝一个新的数组对象出来，长度为size+参数数组的长度。

public boolean addAll(Collection<? extends E> c) {
    Object[] a = c.toArray();
    int numNew = a.length;
    ensureCapacityInternal(size + numNew);  // Increments modCount
    System.arraycopy(a, 0, elementData, size, numNew);
    size += numNew;
    return numNew != 0;
}

在指定位置新增一个集合对象数据，首先判断传入的下标是否越界，然后把数组对象参数的长度+size去判断是否需要扩容，接着去判断size是否大于参数下标，如果大于就把index之后的数据移动到index+参数数据的长度之后下标，最后再把参数数组拷贝到移动之后的数组中，把size设置为size+参数数组的长度。

public boolean addAll(int index, Collection<? extends E> c) {
    rangeCheckForAdd(index);

    Object[] a = c.toArray();
    int numNew = a.length;
    ensureCapacityInternal(size + numNew);  // Increments modCount

    int numMoved = size - index;
    if (numMoved > 0)
        System.arraycopy(elementData, index, elementData, index + numNew,
                         numMoved);

    System.arraycopy(a, 0, elementData, index, numNew);
    size += numNew;
    return numNew != 0;
}

移除参数中指定的集合数据，首先调用Object.requireNonNull判断该集合不能null否则抛空指针异常，最后调用私有方法batchRemove去做批量移除数据。

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

保留参数中指定的集合数据，首先调用Object.requireNonNull判断该集合不能null否则抛空指针异常，最后调用私有方法batchRemove去做批量移除不是参数集合中其他数据。

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

根据传入的下标调用内部类ListItr(index)构造函数新建一个ListItr对象。

public ListIterator<E> listIterator(int index) {
    if (index < 0 || index > size)
        throw new IndexOutOfBoundsException("Index: "+index);
    return new ListItr(index);
}

调用内部类ListItr(index)构造函数新建一个index下标为0的ListItr对象。

public ListIterator<E> listIterator() {
    return new ListItr(0);
}

调用内部类构造函数Itr(),新建一个Itr对象。

public Iterator<E> iterator() {
    return new Itr();
}

返回指定区间的集合，左闭右开，取出之后他也有对其的一系列操作
- ```
private class SubList extends AbstractList<E> implements RandomAccess 
```

public List<E> subList(int fromIndex, int toIndex) {
    subListRangeCheck(fromIndex, toIndex, size);
    return new SubList(this, 0, fromIndex, toIndex);
}

subList下标越界异常处理

static void subListRangeCheck(int fromIndex, int toIndex, int size) {
    if (fromIndex < 0)
        throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
    if (toIndex > size)
        throw new IndexOutOfBoundsException("toIndex = " + toIndex);
    if (fromIndex > toIndex)
        throw new IllegalArgumentException("fromIndex(" + fromIndex +
                                           ") > toIndex(" + toIndex + ")");
}

这个是一个forEach方法循环调用函数接口Consumer.accept方法处理，函数接口就是利用labom表达式处理的。

@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();
    }
}

public static void main(String[] args) {
    List<Object> list = new ArrayList<>();
    list.add(1);
    list.add(2);
    list.add(3);
    list.add("你");
    list.forEach(item-> System.out.println(item));//1 2 3 你
    list.forEach(item->{
        if("你".equals(item)){
            System.out.println(item);//你
        }
    });
}

@Override
public Spliterator<E> spliterator() {
    return new ArrayListSpliterator<>(this, 0, -1, 0);
}

@Override
public Spliterator<E> spliterator() {
    return new ArrayListSpliterator<>(this, 0, -1, 0);
}

@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;
}

@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++;
}

集合的排序方法也是利用的函数接口Comparator，调用Arrays.sort处理。

@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++;
    }
}

三、类内部方法

如果elementData为空，则返回Math.max(DEFAULT_CAPACITY, minCapacity)，默认容量和数组长度谁大选谁
- 不为空，则返回size

private static int calculateCapacity(Object[] elementData, int minCapacity) {
    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
        return Math.max(DEFAULT_CAPACITY, minCapacity);
    }
    return minCapacity;
}

这四个方法就是对使用add方法然后数组进行一个扩容

private void ensureCapacityInternal(int minCapacity) {
    ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}

//如果elementData为空，则返回Math.max(DEFAULT_CAPACITY, minCapacity)，默认容量和数组长度谁大选谁,不为空，则返回size
private static int calculateCapacity(Object[] elementData, int minCapacity) {
    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
        return Math.max(DEFAULT_CAPACITY, minCapacity);
    }
    return minCapacity;
}

//ensureExplicitCapacity:确保明确的容量
private void ensureExplicitCapacity(int minCapacity) {
    modCount++;

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

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

//对数据进行扩容，1.5倍
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;
    }

它跳过边界检查并且不返回删除的值。用于remove(Object o)

 /*
     * Private remove method that skips bounds checking and does not
     * return the value removed.
     * 它跳过边界检查并且不返回删除的值。用于remove(Object o)
     */  
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
    }

从此列表中删除索引介于之间的所有元素

protected void removeRange(int fromIndex, int toIndex) {
    modCount++;
    int numMoved = size - toIndex;
    System.arraycopy(elementData, toIndex, elementData, fromIndex,
                     numMoved);

    // clear to let GC do its work
    int newSize = size - (toIndex-fromIndex);
    for (int i = newSize; i < size; i++) {
        elementData[i] = null;
    }
    size = newSize;
}

下标检查是否越界

private void rangeCheck(int index) {
    if (index >= size)
        throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}

判断下标是否小于0 ，或越界

	/**
     * A version of rangeCheck used by add and addAll.
     *add和addAll使用的rangeCheck版本。
     */
private void rangeCheckForAdd(int index) {
    if (index > size || index < 0)
        throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}

越界异常返回错误信息

private String outOfBoundsMsg(int index) {
    return "Index: "+index+", Size: "+size;
}

批量移除数据，循环判断参数集合c是否包含element数组中的数据，如果传入的complement就是记录不包含的数据，否则记录的就是包含的数据，最后会把匹配的数据之外的所有数据都设置为null,重新设置一下集合的大小size,且把是否修改标识设置为已修改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;
}

这个是手动序列化数据的方法把数据序列化到ObjectOutputStream中，首先记录修改次数给expModCount属性最后会判断这个属性与modCount属性是否相等，如果不相等就抛出ConcurrentModificationException异常，接着调用s.defaultWriteObject()这个方法主要是序列化没有被transient修饰的其他数据，接着序列化数组的大小s.writeInt(size)，最后循环序列化数组的数据。

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();
    }
}

从ObjectInputStream流中反序列化数据出来，首先调用s.defaultReadObject()反序列化不是transient修饰的数据，接着执行s.readInt()这个方法被注释为可以忽略，再根据反序列化出来的数组大小判读是否需要扩容，如果需要扩容就先扩容，最后再把被transient修饰的elementData数据反序列化出来保存到扩容后的数组对象里。

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
        int capacity = calculateCapacity(elementData, size);
        SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, 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();
        }
    }
}

四、类

SubList类

private class SubList extends AbstractList<E> implements RandomAccess {
    private final AbstractList<E> parent;
    private final int parentOffset;
    private final int offset;
    int size;

    SubList(AbstractList<E> parent,
            int offset, int fromIndex, int toIndex) {
        this.parent = parent;
        this.parentOffset = fromIndex;
        this.offset = offset + fromIndex;
        this.size = toIndex - fromIndex;
        this.modCount = ArrayList.this.modCount;
    }

    public E set(int index, E e) {
        rangeCheck(index);
        checkForComodification();
        E oldValue = ArrayList.this.elementData(offset + index);
        ArrayList.this.elementData[offset + index] = e;
        return oldValue;
    }

    public E get(int index) {
        rangeCheck(index);
        checkForComodification();
        return ArrayList.this.elementData(offset + index);
    }

    public int size() {
        checkForComodification();
        return this.size;
    }

    public void add(int index, E e) {
        rangeCheckForAdd(index);
        checkForComodification();
        parent.add(parentOffset + index, e);
        this.modCount = parent.modCount;
        this.size++;
    }

    public E remove(int index) {
        rangeCheck(index);
        checkForComodification();
        E result = parent.remove(parentOffset + index);
        this.modCount = parent.modCount;
        this.size--;
        return result;
    }

    protected void removeRange(int fromIndex, int toIndex) {
        checkForComodification();
        parent.removeRange(parentOffset + fromIndex,
                           parentOffset + toIndex);
        this.modCount = parent.modCount;
        this.size -= toIndex - fromIndex;
    }

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

    public boolean addAll(int index, Collection<? extends E> c) {
        rangeCheckForAdd(index);
        int cSize = c.size();
        if (cSize==0)
            return false;

        checkForComodification();
        parent.addAll(parentOffset + index, c);
        this.modCount = parent.modCount;
        this.size += cSize;
        return true;
    }

    public Iterator<E> iterator() {
        return listIterator();
    }

    public ListIterator<E> listIterator(final int index) {
        checkForComodification();
        rangeCheckForAdd(index);
        final int offset = this.offset;

        return new ListIterator<E>() {
            int cursor = index;
            int lastRet = -1;
            int expectedModCount = ArrayList.this.modCount;

            public boolean hasNext() {
                return cursor != SubList.this.size;
            }

            @SuppressWarnings("unchecked")
            public E next() {
                checkForComodification();
                int i = cursor;
                if (i >= SubList.this.size)
                    throw new NoSuchElementException();
                Object[] elementData = ArrayList.this.elementData;
                if (offset + i >= elementData.length)
                    throw new ConcurrentModificationException();
                cursor = i + 1;
                return (E) elementData[offset + (lastRet = i)];
            }

            public boolean hasPrevious() {
                return cursor != 0;
            }

            @SuppressWarnings("unchecked")
            public E previous() {
                checkForComodification();
                int i = cursor - 1;
                if (i < 0)
                    throw new NoSuchElementException();
                Object[] elementData = ArrayList.this.elementData;
                if (offset + i >= elementData.length)
                    throw new ConcurrentModificationException();
                cursor = i;
                return (E) elementData[offset + (lastRet = i)];
            }

            @SuppressWarnings("unchecked")
            public void forEachRemaining(Consumer<? super E> consumer) {
                Objects.requireNonNull(consumer);
                final int size = SubList.this.size;
                int i = cursor;
                if (i >= size) {
                    return;
                }
                final Object[] elementData = ArrayList.this.elementData;
                if (offset + i >= elementData.length) {
                    throw new ConcurrentModificationException();
                }
                while (i != size && modCount == expectedModCount) {
                    consumer.accept((E) elementData[offset + (i++)]);
                }
                // update once at end of iteration to reduce heap write traffic
                lastRet = cursor = i;
                checkForComodification();
            }

            public int nextIndex() {
                return cursor;
            }

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

            public void remove() {
                if (lastRet < 0)
                    throw new IllegalStateException();
                checkForComodification();

                try {
                    SubList.this.remove(lastRet);
                    cursor = lastRet;
                    lastRet = -1;
                    expectedModCount = ArrayList.this.modCount;
                } catch (IndexOutOfBoundsException ex) {
                    throw new ConcurrentModificationException();
                }
            }

            public void set(E e) {
                if (lastRet < 0)
                    throw new IllegalStateException();
                checkForComodification();

                try {
                    ArrayList.this.set(offset + lastRet, e);
                } catch (IndexOutOfBoundsException ex) {
                    throw new ConcurrentModificationException();
                }
            }

            public void add(E e) {
                checkForComodification();

                try {
                    int i = cursor;
                    SubList.this.add(i, e);
                    cursor = i + 1;
                    lastRet = -1;
                    expectedModCount = ArrayList.this.modCount;
                } catch (IndexOutOfBoundsException ex) {
                    throw new ConcurrentModificationException();
                }
            }

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

    public List<E> subList(int fromIndex, int toIndex) {
        subListRangeCheck(fromIndex, toIndex, size);
        return new SubList(this, offset, fromIndex, toIndex);
    }

    private void rangeCheck(int index) {
        if (index < 0 || index >= this.size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }

    private void rangeCheckForAdd(int index) {
        if (index < 0 || index > this.size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }

    private String outOfBoundsMsg(int index) {
        return "Index: "+index+", Size: "+this.size;
    }

    private void checkForComodification() {
        if (ArrayList.this.modCount != this.modCount)
            throw new ConcurrentModificationException();
    }

    public Spliterator<E> spliterator() {
        checkForComodification();
        return new ArrayListSpliterator<E>(ArrayList.this, offset,
                                           offset + this.size, this.modCount);
    }
}

private class Itr implements Iterator<E> {
    int cursor;       // index of next element to return
    int lastRet = -1; // index of last element returned; -1 if no such
    int expectedModCount = modCount;

    Itr() {}

    public boolean hasNext() {
        return cursor != size;
    }

    @SuppressWarnings("unchecked")
    public E next() {
        checkForComodification();
        int i = cursor;
        if (i >= size)
            throw new NoSuchElementException();
        Object[] elementData = ArrayList.this.elementData;
        if (i >= elementData.length)
            throw new ConcurrentModificationException();
        cursor = i + 1;
        return (E) elementData[lastRet = i];
    }

    public void remove() {
        if (lastRet < 0)
            throw new IllegalStateException();
        checkForComodification();

        try {
            ArrayList.this.remove(lastRet);
            cursor = lastRet;
            lastRet = -1;
            expectedModCount = modCount;
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }

ListItr

private class ListItr extends Itr implements ListIterator<E> {
    ListItr(int index) {
        super();
        cursor = index;
    }

    public boolean hasPrevious() {
        return cursor != 0;
    }

    public int nextIndex() {
        return cursor;
    }

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

    @SuppressWarnings("unchecked")
    public E previous() {
        checkForComodification();
        int i = cursor - 1;
        if (i < 0)
            throw new NoSuchElementException();
        Object[] elementData = ArrayList.this.elementData;
        if (i >= elementData.length)
            throw new ConcurrentModificationException();
        cursor = i;
        return (E) elementData[lastRet = i];
    }

    public void set(E e) {
        if (lastRet < 0)
            throw new IllegalStateException();
        checkForComodification();

        try {
            ArrayList.this.set(lastRet, e);
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }

    public void add(E e) {
        checkForComodification();

        try {
            int i = cursor;
            ArrayList.this.add(i, e);
            cursor = i + 1;
            lastRet = -1;
            expectedModCount = modCount;
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }
}

ArrayListSpliterator

static final class ArrayListSpliterator<E> implements Spliterator<E> {

    /*
     * If ArrayLists were immutable, or structurally immutable (no
     * adds, removes, etc), we could implement their spliterators
     * with Arrays.spliterator. Instead we detect as much
     * interference during traversal as practical without
     * sacrificing much performance. We rely primarily on
     * modCounts. These are not guaranteed to detect concurrency
     * violations, and are sometimes overly conservative about
     * within-thread interference, but detect enough problems to
     * be worthwhile in practice. To carry this out, we (1) lazily
     * initialize fence and expectedModCount until the latest
     * point that we need to commit to the state we are checking
     * against; thus improving precision.  (This doesn't apply to
     * SubLists, that create spliterators with current non-lazy
     * values).  (2) We perform only a single
     * ConcurrentModificationException check at the end of forEach
     * (the most performance-sensitive method). When using forEach
     * (as opposed to iterators), we can normally only detect
     * interference after actions, not before. Further
     * CME-triggering checks apply to all other possible
     * violations of assumptions for example null or too-small
     * elementData array given its size(), that could only have
     * occurred due to interference.  This allows the inner loop
     * of forEach to run without any further checks, and
     * simplifies lambda-resolution. While this does entail a
     * number of checks, note that in the common case of
     * list.stream().forEach(a), no checks or other computation
     * occur anywhere other than inside forEach itself.  The other
     * less-often-used methods cannot take advantage of most of
     * these streamlinings.
     */

    private final ArrayList<E> list;
    private int index; // current index, modified on advance/split
    private int fence; // -1 until used; then one past last index
    private int expectedModCount; // initialized when fence set

    /** Create new spliterator covering the given  range */
    ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
                         int expectedModCount) {
        this.list = list; // OK if null unless traversed
        this.index = origin;
        this.fence = fence;
        this.expectedModCount = expectedModCount;
    }

    private int getFence() { // initialize fence to size on first use
        int hi; // (a specialized variant appears in method forEach)
        ArrayList<E> lst;
        if ((hi = fence) < 0) {
            if ((lst = list) == null)
                hi = fence = 0;
            else {
                expectedModCount = lst.modCount;
                hi = fence = lst.size;
            }
        }
        return hi;
    }

    public ArrayListSpliterator<E> trySplit() {
        int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
        return (lo >= mid) ? null : // divide range in half unless too small
            new ArrayListSpliterator<E>(list, lo, index = mid,
                                        expectedModCount);
    }

    public boolean tryAdvance(Consumer<? super E> action) {
        if (action == null)
            throw new NullPointerException();
        int hi = getFence(), i = index;
        if (i < hi) {
            index = i + 1;
            @SuppressWarnings("unchecked") E e = (E)list.elementData[i];
            action.accept(e);
            if (list.modCount != expectedModCount)
                throw new ConcurrentModificationException();
            return true;
        }
        return false;
    }

    public void forEachRemaining(Consumer<? super E> action) {
        int i, hi, mc; // hoist accesses and checks from loop
        ArrayList<E> lst; Object[] a;
        if (action == null)
            throw new NullPointerException();
        if ((lst = list) != null && (a = lst.elementData) != null) {
            if ((hi = fence) < 0) {
                mc = lst.modCount;
                hi = lst.size;
            }
            else
                mc = expectedModCount;
            if ((i = index) >= 0 && (index = hi) <= a.length) {
                for (; i < hi; ++i) {
                    @SuppressWarnings("unchecked") E e = (E) a[i];
                    action.accept(e);
                }
                if (lst.modCount == mc)
                    return;
            }
        }
        throw new ConcurrentModificationException();
    }

    public long estimateSize() {
        return (long) (getFence() - index);
    }

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

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ArrayList源码分析

ArrayList

一、成员变量

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