JDK源码学习札记-ArrayList\Vector

JDK源码学习笔记-ArrayList\Vector
1、ArrayList容量变化的规则

   public void ensureCapacity(int minCapacity) {modCount++;int oldCapacity = elementData.length;if (minCapacity > oldCapacity) {    Object oldData[] = elementData;    int newCapacity = (oldCapacity * 3)/2 + 1;        if (newCapacity < minCapacity)newCapacity = minCapacity;            // minCapacity is usually close to size, so this is a win:            elementData = Arrays.copyOf(elementData, newCapacity);}    }

可以看出ArrayList扩容：（旧容量*3）/2 + 1，这样做的依据是什么？查资料也没找到答案，有知道的告诉下呗~
2、AyyayList指定位置的插入操作

    public void add(int index, E element) {if (index > size || index < 0)    throw new IndexOutOfBoundsException("Index: "+index+", Size: "+size);ensureCapacity(size+1);  // Increments modCount!![color=red]System.arraycopy(elementData, index, elementData, index + 1, size - index);[/color]elementData[index] = element;size++;    }

同理，删除操作remove(int index)也是做了一次这样的拷贝。
3、Vector容量变化规则

    private void ensureCapacityHelper(int minCapacity) {int oldCapacity = elementData.length;if (minCapacity > oldCapacity) {    Object[] oldData = elementData;    int newCapacity = (capacityIncrement > 0) ?(oldCapacity + capacityIncrement) : (oldCapacity * 2);        if (newCapacity < minCapacity) {newCapacity = minCapacity;    }            elementData = Arrays.copyOf(elementData, newCapacity);}    }

当capacityIncrement变量大于0时则按照该变量值进行扩容，否则翻倍扩容（注意此处与ArrayList的区别）。
4、注意Vector中capacity()与size()的区别：
capacity()返回Vector当前容量；size()返回实际存储的元素长度。
5、Vector查重

public synchronized boolean retainAll(Collection<?> c)  {        return super.retainAll(c);    }

ArrayList同样拥有！
5、AbstractList中的equals()方法

ListIterator e2 = ((List) o).listIterator();

所以下面这段代码：

        ArrayList<Integer> temp1 = new ArrayList<Integer>();        Vector<Integer> temp2 = new Vector<Integer>();                Integer e1 = new Integer(1);        Integer e2 = new Integer(2);                temp1.add(e1);        temp1.add(e2);                temp2.add(e1);        temp2.add(e2);                if(temp2.equals(temp1)) {            System.out.println("equals");        }else {            System.out.println("not equals");        }

输出结果是“equals”!

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