ArrayList 源碼解讀
阿新 • • 發佈:2017-09-24
transient implement max fault blog ans 容量 system arrays
ArrayList 源碼解讀 基於JDk 1.7.0_80
public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable
ArrayList的底層是使用數組實現的,因為數組的容量是固定的,要實現可變容量List,所以一定存在著容量檢測,數組復制等方法。
對象屬性
/** * 默認大小 */ private static final int DEFAULT_CAPACITY = 10;/** * 空對象數組 ,用來做比較 */ private static final Object[] EMPTY_ELEMENTDATA = {}; /** * 存儲數據的數組 */ private transient Object[] elementData; /** * 大小 */ private int size;
構造方法
/** * 指定大小*/ public ArrayList(int initialCapacity) { super();if (initialCapacity < 0) throw new IllegalArgumentException("Illegal Capacity: "+ initialCapacity); this.elementData = new Object[initialCapacity]; } /** * 默認 */ public ArrayList() { super(); this.elementData = EMPTY_ELEMENTDATA; } /** * 傳入一個Collection*/ public ArrayList(Collection<? extends E> c) { elementData = c.toArray(); size = elementData.length; // c.toArray might (incorrectly) not return Object[] (see 6260652) if (elementData.getClass() != Object[].class) elementData = Arrays.copyOf(elementData, size, Object[].class); }
add 方法
public boolean add(E e) { ensureCapacityInternal(size + 1); // Increments modCount!! elementData[size++] = e; return true; } // 在指定位置添加對象 public void add(int index, E element) { // 判斷添加的位置是否合理 rangeCheckForAdd(index); ensureCapacityInternal(size + 1); // Increments modCount!! System.arraycopy(elementData, index, elementData, index + 1, size - index); elementData[index] = element; size++; } //判斷是否是空數組 private void ensureCapacityInternal(int minCapacity) { if (elementData == EMPTY_ELEMENTDATA) { minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity); } ensureExplicitCapacity(minCapacity); } //判斷是否達到了數組的容量 private void ensureExplicitCapacity(int minCapacity) { modCount++; // overflow-conscious code if (minCapacity - elementData.length > 0) grow(minCapacity); } //增加容量 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); }
remove 方法
/** * Removes the element at the specified position in this list. */ public E remove(int index) { // 檢測是否越界 rangeCheck(index); modCount++; E oldValue = elementData(index); int numMoved = size - index - 1; if (numMoved > 0) //數組移動 System.arraycopy(elementData, index+1, elementData, index,numMoved); //最後一位設為null elementData[--size] = null; // clear to let GC do its work return oldValue; } /** * Removes the first occurrence of the specified element from this list, */ 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; } 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 } private void rangeCheck(int index) { if (index >= size) throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); }
get方法
public E get(int index) { rangeCheck(index); return elementData(index); }
set方法
public E set(int index, E element) { rangeCheck(index); E oldValue = elementData(index); elementData[index] = element; return oldValue; }
內部類Itr 實現了Iterator接口 ,實現了 next() hasNext() remove() 三個方法
public Iterator<E> iterator() {
return new Itr();
}
/**
* An optimized version of AbstractList.Itr
*/
private class Itr implements Iterator<E> {
// 下一個返回的位置
int cursor; // index of next element to return
// 上次返回的位置
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;
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();
}
}
//當你在使用叠代器時,不能使用 使用 set add 等方法,改變 存儲的數據
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
ListItr 內部類
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(); } } }
ArrayList 源碼解讀