JavaSE_坚持读源码_ArrayList对象_Java1.7

底层的数组对象

1 /**
2  * The array buffer into which the elements of the ArrayList are stored.
3  * The capacity of the ArrayList is the length of this array buffer. Any
4  * empty ArrayList with elementData == EMPTY_ELEMENTDATA will be expanded to
5  * DEFAULT_CAPACITY when the first element is added.
6  */
7  //ArrayList底层的数组对象
8 private transient Object[] elementData;

get(int index) 方法

 1     public E get(int index) {
 2     //先对角标进行校验，看看是否越界
 3         rangeCheck(index);
 4 
 5         return elementData(index);
 6     }
 7 
 8     //throws an ArrayIndexOutOfBoundsException if index is negative
 9     //如果index是负数，抛出ArrayIndexOutOfBoundsException
10     private void rangeCheck(int index) {
11         if (index >= size)
12             throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
13     }
14 
15     //真正的获取元素的方法，就是从底层的数据库获取index处的元素，返回值E是由ArrayList的泛型指定
16     E elementData(int index) {
17         return (E) elementData[index];
18     }

set(int index, E element)

 1     public E set(int index, E element) {
 2     //先对角标进行校验，看看是否越界
 3         rangeCheck(index);
 4     
 5     //取出以前位于该指定位置上的元素
 6         E oldValue = elementData(index);
 7     //将数组位于index位置上的元素设置为element
 8         elementData[index] = element;
 9     //将以前位于该指定位置上的元素返回
10         return oldValue;
11     }