ArrayList原始碼淺析
阿新 • • 發佈：2018-12-13
動態陣列的列表
新增元素
// 增加一個元素 public boolean add(E e) { // 確保陣列容量足夠 ensureCapacityInternal(size + 1); // Increments modCount!! // 增加元素 elementData[size++] = e; return true; } // 確保陣列有足夠的容量 private void ensureCapacityInternal(int minCapacity) { // 如果當前是空陣列 if (elementData == EMPTY_ELEMENTDATA) { minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity); } // 確定明確的容量 ensureExplicitCapacity(minCapacity); } // 確定明確的容量 private void ensureExplicitCapacity(int minCapacity) { modCount++; // overflow-conscious code if (minCapacity - elementData.length > 0) // 如果當前容量不滿足最小容量要求，則對陣列進行擴容 grow(minCapacity); } // 對陣列進行擴容 private void grow(int minCapacity) { // overflow-conscious code int oldCapacity = elementData.length; // 新的容量等於舊的容量乘以1.5 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: // 建立長度為newCapacity的陣列，並複製舊的陣列值到新的陣列中，elementData指向新建立的陣列，完成陣列的擴容 elementData = Arrays.copyOf(elementData, newCapacity); }
新增元素到指定位置
// 增加元素到指定位置 public void add(int index, E element) { if (index > size || index < 0) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); // 判斷是否需要擴容 ensureCapacityInternal(size + 1); // Increments modCount!! // 將index及其後邊的所有元素整塊後移一位，空出index位置 System.arraycopy(elementData, index, elementData, index + 1, size - index); // 設定index位置的元素 elementData[index] = element; size++; }
刪除索引位置的元素
// 刪除指定位置的元素 public E remove(int index) { if (index >= size) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); modCount++; // 找到刪除的元素 E oldValue = (E) elementData[index]; int numMoved = size - index - 1; if (numMoved > 0) // 將index後面元素向前移動一位 System.arraycopy(elementData, index+1, elementData, index, numMoved); // 釋放引用 elementData[--size] = null; // clear to let GC do its work // 返回被刪除的元素 return oldValue; }
刪除某個具體的元素
// 刪除某個元素
public boolean remove(Object o) {
// for迴圈查詢相等的元素，找到對應的索引下標，並通過fastRemove方法刪除該元素
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;
}
// 快速刪除索引位置的元素
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
}查詢某個索引位置的元素
// 獲取指定索引位置的元素
public E get(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
return (E) elementData[index];
}修改某個索引位置的元素
// 修改指定索引位置的元素
public E set(int index, E element) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
E oldValue = (E) elementData[index];
elementData[index] = element;
// 返回被替換掉的元素
return oldValue;
}轉變為陣列
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}
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;
}equals方法來自AbstractList，比較的是相同索引位置的元素是否都equals。
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof List))
return false;
ListIterator<E> e1 = listIterator();
ListIterator e2 = ((List) o).listIterator();
while (e1.hasNext() && e2.hasNext()) {
E o1 = e1.next();
Object o2 = e2.next();
if (!(o1==null ? o2==null : o1.equals(o2)))
return false;
}
return !(e1.hasNext() || e2.hasNext());
}迭代器
// 返回一個用於迭代遍歷物件
public Iterator<E> iterator() {
return new Itr();
}Itr是ArrayList的內部類，Itr只能獲得從索引位置為0開始向後的遍歷
private class Itr implements Iterator<E> {
// The "limit" of this iterator. This is the size of the list at the time the
// iterator was created. Adding & removing elements will invalidate the iteration
// anyway (and cause next() to throw) so saving this value will guarantee that the
// value of hasNext() remains stable and won't flap between true and false when elements
// are added and removed from the list.
protected int limit = ArrayList.this.size;
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;
// 判斷當前還有下一個元素
public boolean hasNext() {
return cursor < limit;
}
@SuppressWarnings("unchecked")
// 獲取下一個元素
public E next() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
int i = cursor;
if (i >= limit)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[lastRet = i];
}
// 移除next方法返回的元素
public void remove() {
// remove方法會對lastRet進行重置為-1，初始化也為-1
// remove方法必須有一個next相對應，否則會丟擲異常
if (lastRet < 0)
throw new IllegalStateException();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
try {
// 刪除next方法返回的元素
ArrayList.this.remove(lastRet);
cursor = lastRet;
// 重置lastRet
lastRet = -1;
// 由於刪除了元素，對陣列進行了操作，需要更新expectedModCount以及limit
expectedModCount = modCount;
limit--;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
@Override
@SuppressWarnings("unchecked")
public void forEachRemaining(Consumer<? super E> consumer) {
Objects.requireNonNull(consumer);
final int size = ArrayList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length) {
throw new ConcurrentModificationException();
}
while (i != size && modCount == expectedModCount) {
consumer.accept((E) elementData[i++]);
}
// update once at end of iteration to reduce heap write traffic
cursor = i;
lastRet = i - 1;
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}ListItr是可以在任意索引位置向前向後的遍歷
public ListIterator<E> listIterator() {
return new ListItr(0);
}
private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
super();
cursor = index;
}
// 當前索引位置前面是否有元素
public boolean hasPrevious() {
return cursor != 0;
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor - 1;
}
@SuppressWarnings("unchecked")
// 獲取前面的元素
public E previous() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
int i = cursor - 1;
if (i < 0)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i;
// 返回當前索引位置前面的元素
return (E) elementData[lastRet = i];
}
// 修改lastRet前一步操作的索引位置的元素值
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
try {
ArrayList.this.set(lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
// 新增元素
public void add(E e) {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
try {
int i = cursor;
ArrayList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
// 更新expectedModCount和limit
expectedModCount = modCount;
limit++;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}子列表
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) {
if (index < 0 || index >= this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
E oldValue = (E) ArrayList.this.elementData[offset + index];
ArrayList.this.elementData[offset + index] = e;
return oldValue;
}
public E get(int index) {
if (index < 0 || index >= this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
return (E) ArrayList.this.elementData[offset + index];
}
public int size() {
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
return this.size;
}
public void add(int index, E e) {
if (index < 0 || index > this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
parent.add(parentOffset + index, e);
this.modCount = parent.modCount;
this.size++;
}
public E remove(int index) {
if (index < 0 || index >= this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
E result = parent.remove(parentOffset + index);
this.modCount = parent.modCount;
this.size--;
return result;
}
protected void removeRange(int fromIndex, int toIndex) {
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
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) {
if (index < 0 || index > this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
int cSize = c.size();
if (cSize==0)
return false;
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
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) {
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
if (index < 0 || index > this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(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() {
if (expectedModCount != ArrayList.this.modCount)
throw new ConcurrentModificationException();
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() {
if (expectedModCount != ArrayList.this.modCount)
throw new ConcurrentModificationException();
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;
if (expectedModCount != ArrayList.this.modCount)
throw new ConcurrentModificationException();
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor - 1;
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
if (expectedModCount != ArrayList.this.modCount)
throw new ConcurrentModificationException();
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();
if (expectedModCount != ArrayList.this.modCount)
throw new ConcurrentModificationException();
try {
ArrayList.this.set(offset + lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
if (expectedModCount != ArrayList.this.modCount)
throw new ConcurrentModificationException();
try {
int i = cursor;
SubList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
expectedModCount = ArrayList.this.modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList(this, offset, fromIndex, toIndex);
}
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+this.size;
}
public Spliterator<E> spliterator() {
if (modCount != ArrayList.this.modCount)
throw new ConcurrentModificationException();
return new ArrayListSpliterator<E>(ArrayList.this, offset,
offset + this.size, this.modCount);
}
}