System.arraycopy 怎么使用的？

前言：看 ArrayList 的源码，发现 remove 方法主要依赖了 System.arraycopy() 方法实现的。所以需要了解一下这个方法如何使用。转载请注明出处：https://www.cnblogs.com/yuxiaole/p/9951819.html

源码

带注释的源码：

    /**
     * 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.
     * <

不带注释的源码：

    public static native void arraycopy(Object src,  int  srcPos,
                                        Object dest, int destPos,
                                        int length);

参数解释：　　

　　src: 源数组； 

　　srcPos: 源数组要复制的起始位置；

　　 dest: 目的数组； 

　　destPos: 目的数组放置的起始位置； 

　　length: 复制的长度。

从源码注释中就可以看出

　　1、拷贝过程：将 src 数组的下标为 srcPos 到 srcPos + length - 1 拷贝到 dest 数组下标为 destPos 到 destPos + length- 1 的位置。

　　2、这个也支持 src 和 dest 为同一个数组，这时会将原数组拷贝到临时数组里，然后再将临时数组的数据拷贝到目标数组。

　　3、如果 src 或者 dest 为 null ，则会抛空指针异常。

　　4、如果 src 或者 dest 不是数组，则会抛出 ArrayStoreException。

　　5、src，dest 不是同类型或者可以进行转换的数组，则会抛出 ArrayStoreException。

　　6、如果 srcPos + length > length或者 destPos + lenght > length，则会抛出 IndexOutOfBoundsException。　　

测试：

 

转载请注明出处：https://www.cnblogs.com/yuxiaole/p/9951819.html