ArrayList源码分析_JDK1.8.0_191

ArrayList JDK1.8.0_191

---

基于数组实现

允许null值

不是线程安全

Vector是ArrayList的线程安全版本

---

ArrayList的变量

transient Object[] elementData;

---

 ArrayList的方法

1.add()：添加元素

public boolean add(E e) {
    ensureCapacityInternal(size + 1);  // Increments modCount!!
    elementData[size++] = e;
    return true;
}

2.grow()：扩容

private void grow(int minCapacity) {
    // overflow-conscious code
    int oldCapacity = elementData.length;
    //扩容为原来的1.5倍
    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);
}

3.elementData()：获取节点值

E elementData(int index) {
    return (E) elementData[index];
}

4.set()：修改节点值

public E set(int index, E element) {
    rangeCheck(index);
    //获取旧值
    E oldValue = elementData(index);
    //修改为新值
    elementData[index] = element;
    return oldValue;
}

5.remove()：删除节点

public E remove(int index) {
    rangeCheck(index);
    modCount++;
    E oldValue = elementData(index);
    int numMoved = size - index - 1;
    if (numMoved > 0)
        //移动节点（复制节点）
        System.arraycopy(elementData, index+1, elementData, index,
                         numMoved);
    //使得被删除节点可以被GC
    elementData[--size] = null; // clear to let GC do its work
    return oldValue;
}