jdk源码阅读——ArrayList

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。