byte数组快速拷贝，byte数组合并，System.arraycopy详解

叁歲伎倆 2021-09-21 16:20 393阅读 0赞

> **博客来源：**
> 
> 项目过程中用到byte\[\]数组相加问题，给出两个byte\[\] 需要合并成一个byte\[\]进行计算…那么需求来了……数据量达10W级，怎么合并

###  调用系统自带方法（System.arraycopy） ###

参考程序

@org.junit.Test
    public void fun(){
        //创建一个存储被拷贝的字节数组，长度一定要比被拷贝字节数组大
        byte[] bytes = new byte[20];
        //创建一个需要字节拷贝的数组
        byte[] byte_name = "xiaoming".getBytes();
        //调用系统方法进行拷贝
        System.arraycopy(byte_name, 0, bytes, 5, byte_name.length);
        //输出原字节数组，两者进行比较
        for (byte bb :byte_name) {
            System.out.print(bb);
        }
        //换行
        System.out.println();
        //输出被拷贝的数组，两者进行比较
        for (byte bb :bytes) {
            System.out.print(bb);
        }
    }

运行结果，已经按照程序要就进行拷贝

![20210203183911657.png][]

### 下面进行详细介绍下，系统方法  （System.arraycopy） ###

> **简单用法：**
> 
> java.lang.System public static void
> 
> arraycopy(@NotNull     Object src,           被拷贝的字节数组  
>                                               int srcPos,          从被拷贝的字节数组的第几位开始拷贝  
>                                               @NotNull Object dest,    拷贝到这个字节数组中  
>                                               int destPos,        从第几位开始拷贝被拷贝的数组  
>                                               int length            拷贝多少位被拷贝的字节数组

### 来！看一下官方解释， 其实也就是上面的解释，加之上面的程序，尝试几次就好啦 ###

> java.lang.System public static void arraycopy(@NotNull Object src,  
>                                                          int srcPos,  
>                                                          @NotNull Object dest,  
>                                                          int destPos,  
>                                                          int length)  
> 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 src to the destination array referenced by dest. The number of components copied is equal to the length argument. The components at positions srcPos through srcPos+length-1 in the source array are copied into positions destPos through destPos+length-1, respectively, of the destination array.  
> If the src and dest arguments refer to the same array object, then the copying is performed as if the components at positions srcPos through srcPos+length-1 were first copied to a temporary array with length components and then the contents of the temporary array were copied into positions destPos through destPos+length-1 of the destination array.  
> If dest is null, then a NullPointerException is thrown.  
> If src is null, then a NullPointerException is thrown and the destination array is not modified.  
> Otherwise, if any of the following is true, an ArrayStoreException is thrown and the destination is not modified:
> 
>  *      The src argument refers to an object that is not an array.
>  *      The dest argument refers to an object that is not an array.
>  *      The src argument and dest argument refer to arrays whose component types are different primitive types.
>  *      The src argument refers to an array with a primitive component type and the dest argument refers to an array with a reference component type.
>  *      The src argument refers to an array with a reference component type and the dest argument refers to an array with a primitive component type.
> 
> Otherwise, if any of the following is true, an IndexOutOfBoundsException is thrown and the destination is not modified:
> 
>  *      The srcPos argument is negative.
>  *      The destPos argument is negative.
>  *      The length argument is negative.
>  *      srcPos+length is greater than src.length, the length of the source array.
>  *      destPos+length is greater than dest.length, the length of the destination array.
> 
> Otherwise, if any actual component of the source array from position srcPos through srcPos+length-1 cannot be converted to the component type of the destination array by assignment conversion, an ArrayStoreException is thrown. In this case, let k be the smallest nonnegative integer less than length such that src\[srcPos+k\] cannot be converted to the component type of the destination array; when the exception is thrown, source array components from positions srcPos through srcPos+k-1 will already have been copied to destination array positions destPos through destPos+k-1 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.)
> 
> Params:  
>                     src – the source array.  
>                     srcPos – starting position in the source array.  
>                     dest – the destination array.  
>                     destPos – starting position in the destination data.  
>                     length – the number of array elements to be copied.  
>                       
> Throws:  
>                     IndexOutOfBoundsException – if copying would cause access of data outside array bounds.  
>                     ArrayStoreException – if an element in the src array could not be stored into the dest array because of a type mismatch.  
>                     NullPointerException – if either src or dest is null.  
>                       
> External annotations:  
>                     Parameter src: @org.jetbrains.annotations.NotNull  
>                     Parameter dest: @org.jetbrains.annotations.NotNull

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[20210203183911657.png]: /images/20210920/b50ba9baff644b6b8f7238da674ae6af.png
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