System.arraycopy 怎麼使用的？

前言：看 ArrayList 的源碼，發現 remove 方法主要依賴了 System.arraycopy() 方法實現的。因此須要瞭解一下這個方法如何使用。轉載請註明出處：https://www.cnblogs.com/yuxiaole/p/9951819.html

源碼

帶註釋的源碼：

    /**
     * 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.
     * <

View Code

不帶註釋的源碼：

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

參數解釋：　　

　　src: 源數組； 

　　srcPos: 源數組要複製的起始位置；

　　 dest: 目的數組； 

　　destPos: 目的數組放置的起始位置； 

　　length: 複製的長度。

從源碼註釋中就能夠看出

　　一、拷貝過程：將 src 數組的下標爲 srcPos 到 srcPos + length - 1 拷貝到 dest 數組下標爲 destPos 到 destPos + length- 1 的位置。

　　二、這個也支持 src 和 dest 爲同一個數組，這時會將原數組拷貝到臨時數組裏，而後再將臨時數組的數據拷貝到目標數組。

　　三、若是 src 或者 dest 爲 null ，則會拋空指針異常。

　　四、若是 src 或者 dest 不是數組，則會拋出 ArrayStoreException。

　　五、src，dest 不是同類型或者能夠進行轉換的數組，則會拋出 ArrayStoreException。

　　六、若是 srcPos + length > length或者 destPos + lenght > length，則會拋出 IndexOutOfBoundsException。　　

測試：

 

轉載請註明出處：https://www.cnblogs.com/yuxiaole/p/9951819.html