/**

arraycopy(Object src,  int  srcPos, 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. 从指定的 源数组位置 复制到 指定的目标数组的位置 来复制源数组.     * 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 从 源数组src 中复制子序列到 目标数组dest, 子序列的长度由 length参数控制.      * positions srcPos through     * srcPos+length-1 in the source array are copied into     * positions destPos through     * destPos+length-1, respectively, of the destination     * array. 从 src 数组中的 srcPos, srcPos+length-1 的元素将会被复制到 dest 数组的 destPos, destPos+length-1 位置.     * 
     * 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. 如果 src 和 dest 引用的是相同的数组,那么复制的过程就是首先从 数组的 srcPos, srcPos+length-1 复制到 length 长度的临时数组, 然后在从临时数组中拷贝内容到这个数组的 destPos, destPos+length-1 的位置.     * 
     * If dest is null, then a     * NullPointerException is thrown. 如果 dest 是 null, 会抛出 NullPointerException 异常.

* 
 * If src is null, then a * NullPointerException is thrown and the destination * array is not modified. 如果 src 是 null, 也将会抛出 NullPointException 异常,但是并不会改变 dest 的内容. * 
 * Otherwise, if any of the following is true, an * ArrayStoreException is thrown and the destination is * not modified: 另外,下面的情况都会抛出 ArrayStoreException 异常,且都不会修改 dest 的内容. * 
     
       * 
      
The src argument refers to an object that is not an * array. 　　src 引用的对象不是数组. * 
      
The dest argument refers to an object that is not an * array. 　　dest 引用的对象不是数组. * 
      
The src argument and dest argument refer * to arrays whose component types are different primitive types. 　　src 和 dest 原始类型不同. * 
      
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.
     

另外,下面的情况都会抛出 IndexOutOfBoundsException 异常,且都不会修改 dest 的内容.

*  * 
 * Otherwise, if any of the following is true, an * IndexOutOfBoundsException is * thrown and the destination is not modified: * 
     
       * 
      
The srcPos argument is negative. 　　srcPos 是负数. * 
      
The destPos argument is negative. 　　destPos 是负数. * 
      
The length argument is negative. 　　length 是负数. * 
      
srcPos+length is greater than 　　srcPos+length 大于 src 数组的出长度 * src.length, the length of the source array. * 
      
destPos+length is greater than * dest.length, the length of the destination array. 　　destPos+length 大于 dest 数组的长度 * 
     
 * 
 * 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 另外,如果 src 的元素不能转换成 dest 目标的类型,也会抛出 ArrayStoreException 异常. * 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.) 特奶奶的,天书也没说到点子上,白看了.... * * @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 src * array could not be stored into the dest array * because of a type mismatch. * @exception NullPointerException if either src or * dest is null. */ public static native void arraycopy(Object src, int srcPos, Object dest, int destPos, int length);

1 import java.util.Arrays; 2  3 public class ArrayCopyThink { 4  5     public static void main(String[] args) { 6  7         User u1 = new User("test1"); 8         User u2 = new User("test2"); 9         User u3 = new User("test3");10         User u4 = new User("test4");11         User[] users = {u1, u2, u3, u4};12 13         User u5 = new User("ooo");14         System.out.println("源数组 users: " + Arrays.toString(users));15 16         User[] copyUsers = new User[5];17         copyUsers[0] = u5;18         System.out.println("目标数组 copyUsers: " + Arrays.toString(copyUsers));19 20         System.out.println("将源数组的所有元素拷贝到目标数组的后面..");21         System.arraycopy(users, 0, copyUsers, 1, users.length);22 23         System.out.println("源数组 users: " + Arrays.toString(users));24         System.out.println("目标数组 copyUsers: " + Arrays.toString(copyUsers));25 26         System.out.println("更改拷贝数组拷贝过来的第一个元素,");27         copyUsers[1].setName("###");28         System.out.println("源数组 users: " + Arrays.toString(users));29         System.out.println("目标数组 copyUsers: " + Arrays.toString(copyUsers));30 31 32 33 34     }35 36     static class User {37 38         private String name;39 40         public User(String name) {41             this.name = name;42         }43 44         public String getName() {45             return name;46         }47 48         public void setName(String name) {49             this.name = name;50         }51 52         @Override53         public String toString() {54             return "User{" +55                     "name='" + name + '\'' +56                     '}';57         }58     }59 60 }