重要的源码
我认为本身相对比较容易理解 就列举为认为，要了解ArrayList 较重要的方法 该方法使用了9 次
/**
- @param src 源数组。
- @param srcPos 源数组中的起始位置。
- @param dest 目标数组。
- @param destPos 目标数据中的起始位置。
- @param length 要复制的数组元素的数量
- @exception IndexOutOfBoundsException if copying would cause */
public static native void arraycopy(Object src, int srcPos,
Object dest, int destPos,
int length);
我认为大概的意思就是 src 的第 srcPro 个 复制到 dest 的第 destPost 个 lenght 要复制的数组元素的数量
更具体看下面的源码
/**
* Copies an array from the specified source array, beginning at the
* specified position, to the specified position of the destination array.
* A subsequence of array components are copied from the source
* array referenced by <code>src</code> to the destination array
* referenced by <code>dest</code>. The number of components copied is
* equal to the <code>length</code> argument. The components at
* positions <code>srcPos</code> through
* <code>srcPos+length-1</code> in the source array are copied into
* positions <code>destPos</code> through
* <code>destPos+length-1</code>, respectively, of the destination
* array.
* <p>
* If the <code>src</code> and <code>dest</code> arguments refer to the
* same array object, then the copying is performed as if the
* components at positions <code>srcPos</code> through
* <code>srcPos+length-1</code> were first copied to a temporary
* array with <code>length</code> components and then the contents of
* the temporary array were copied into positions
* <code>destPos</code> through <code>destPos+length-1</code> of the
* destination array.
* <p>
* If <code>dest</code> is <code>null</code>, then a
* <code>NullPointerException</code> is thrown.
* <p>
* If <code>src</code> is <code>null</code>, then a
* <code>NullPointerException</code> is thrown and the destination
* array is not modified.
* <p>
* Otherwise, if any of the following is true, an
* <code>ArrayStoreException</code> is thrown and the destination is
* not modified:
* <ul>
* <li>The <code>src</code> argument refers to an object that is not an
* array.
* <li>The <code>dest</code> argument refers to an object that is not an
* array.
* <li>The <code>src</code> argument and <code>dest</code> argument refer
* to arrays whose component types are different primitive types.
* <li>The <code>src</code> argument refers to an array with a primitive
* component type and the <code>dest</code> argument refers to an array
* with a reference component type.
* <li>The <code>src</code> argument refers to an array with a reference
* component type and the <code>dest</code> argument refers to an array
* with a primitive component type.
* </ul>
* <p>
* Otherwise, if any of the following is true, an
* <code>IndexOutOfBoundsException</code> is
* thrown and the destination is not modified:
* <ul>
* <li>The <code>srcPos</code> argument is negative.
* <li>The <code>destPos</code> argument is negative.
* <li>The <code>length</code> argument is negative.
* <li><code>srcPos+length</code> is greater than
* <code>src.length</code>, the length of the source array.
* <li><code>destPos+length</code> is greater than
* <code>dest.length</code>, the length of the destination array.
* </ul>
* <p>
* Otherwise, if any actual component of the source array from
* position <code>srcPos</code> through
* <code>srcPos+length-1</code> cannot be converted to the component
* type of the destination array by assignment conversion, an
* <code>ArrayStoreException</code> is thrown. In this case, let
* <b><i>k</i></b> be the smallest nonnegative integer less than
* length such that <code>src[srcPos+</code><i>k</i><code>]</code>
* cannot be converted to the component type of the destination
* array; when the exception is thrown, source array components from
* positions <code>srcPos</code> through
* <code>srcPos+</code><i>k</i><code>-1</code>
* will already have been copied to destination array positions
* <code>destPos</code> through
* <code>destPos+</code><i>k</I><code>-1</code> and no other
* positions of the destination array will have been modified.
* (Because of the restrictions already itemized, this
* paragraph effectively applies only to the situation where both
* arrays have component types that are reference types.)
*
* @param src the source array.
* @param srcPos starting position in the source array.
* @param dest the destination array.
* @param destPos starting position in the destination data.
* @param length the number of array elements to be copied.
* @exception IndexOutOfBoundsException if copying would cause
* access of data outside array bounds.
* @exception ArrayStoreException if an element in the <code>src</code>
* array could not be stored into the <code>dest</code> array
* because of a type mismatch.
* @exception NullPointerException if either <code>src</code> or
* <code>dest</code> is <code>null</code>.
*/
public static native void arraycopy(Object src, int srcPos,
Object dest, int destPos,
int length);
源码我也看不懂，尴尬！
System (Java Platform SE 8 )
public static void arraycopy(Object src,
int srcPos,
Object dest,
int destPos,
int length)
将指定源数组中的数组从指定位置复制到目标数组的指定位置。 阵列组件的一个子序列被从通过引用的源阵列复制src被引用的目标阵列dest 。 复制的组件数量等于length参数。 源阵列中位置srcPos至srcPos+length-1的组件分别复制到目标阵列的位置destPos至destPos+length-1 。
如果src个dest参数指代相同的数组对象，则被处理是否在位置上的部件进行复印srcPos通过srcPos+length-1首先被复制到一个临时的阵列length组分，然后将临时数组的内容被复制到的位置destPos通过destPos+length-1目标数组的。
如果dest是null ，那么会抛出一个NullPointerException 。
如果src是null ，则抛出一个NullPointerException并且目标数组不被修改。
否则，如果以下任一为真，一个ArrayStoreException抛出和不修改目标：
src参数是指不是数组的对象。dest参数是指不是数组的对象。src参数和dest参数是指组件类型是不同的基本类型的数组。src参数是指具有原始组件类型的数组，dest参数是指具有引用组件类型的数组。src参数是指具有引用组件类型的数组，dest参数是指具有原始组件类型的数组。
否则，如果以下任一为真，一个IndexOutOfBoundsException抛出和不修改目标：
srcPos论点是否定的。destPos论点是否定的。length论点是否定的。srcPos+length大于src.length，源数组的长度。destPos+length大于dest.length，目标数组的长度。
否则，如果来自位置srcPos至srcPos+length-1的源数组的任何实际组件无法通过转换转换为目标数组的组件类型，则抛出ArrayStoreException 。 在这种情况下，令k为比长度小于最小的非负整数，使得src[srcPos+ ķ ]不能转换到组件类型目标数组的; 当抛出异常时，位置srcPos至srcPos+ k -1源阵列组件将已经被复制到目标阵列位置destPos至destPos+ k -1 ，并且目标阵列的其他位置将不会被修改。 （由于限制已经列出，本段仅适用于两个数组都具有引用类型的组件类型的情况。）
