概要

个人观点：集合类和concurrent下的类是java里特别精髓的东西。

类的定义 public class ArrayList<E> extends AbstractList<E> implements List<E>, RandomAccess, Cloneable, java.io.Serializable 类的继承关系 java.lang.Object java.util.AbstractCollection<E> java.util.AbstractList<E> java.util.ArrayList<E> 类的特点

http://blog.csdn.net/u014394255/article/details/53449122

属性

private static final int DEFAULT_CAPACITY = 10;

此属性定义list的默认空间大小

transient Object[] elementData;

此属性有序缓存数组元素，每增加一个元素，则，用transient修饰，表示不会序列化

方法

初始化 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); } }

用指定的初始化容量初始化一个空的list

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

检查list中元素是否为null,或在list中的index

elementData @SuppressWarnings("unchecked") E elementData(int index) { return (E) elementData[index]; }

返回访问操作元素位置对应的value

add 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++; }

添加参数到list中，rangeCheckForAdd方法会index的上下界进行检查

remove 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; }

移除list指定位置的值，并释放gc

线程安全 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(); } } 容量扩充 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); }

设置最小的容量，来扩充list的大小；可以看出，oldCapacity 新增的容量是它的一半。另外，还有一个 hugeCapacity，如果需要扩充的容量比　MAX_ARRAY_SIZE 还大，会调用这个函数，重新调整大小。但再大也大不过　Integer.MAX_VALUE。