都是System.arrayCopy() 效率高，到底有多高呢，拉出来遛遛就知道了：
package JCF.ArrayList;
import java.util.Date;
public class ArrayCopyCompare {
public static void main(String[] args) {
int length = 1000000;
//init
System.out.println("array length : "+length);
int[] array = new int[length];
for(int i = 0 ; i < array.length ; i ++){
array[i] = i;
}
//use method by system
long begin1 = new Date().getTime();
int[] arrayCopyBySystem = new int[length];
System.arraycopy(array, 0, arrayCopyBySystem, 0, array.length);
long end1 = new Date().getTime();
System.out.println("use time by system method : "+(end1 - begin1));
//use method normal
long begin2 = new Date().getTime();
int[] arrayCopyByNormal = new int[length];
for(int i = 0 ; i < arrayCopyByNormal.length ; i ++){
arrayCopyByNormal[i] = array[i];
}
long end2 = new Date().getTime();
System.out.println("use time by narmal method : " +(end2 - begin2));
}
}
常用的数组复制方法就按照循环赋值的防范， 下面列举有不多长度数组的效率比较：
array length : 10000
use time by system method : 0
use time by narmal method : 0
array length : 100000
use time by system method : 0
use time by narmal method : 2
array length : 1000000
use time by system method : 3
use time by narmal method : 5
array length : 10000000
use time by system method : 25
use time by narmal method : 29
array length : 100000000
use time by system method : 279
use time by narmal method : 293
所以在数组长度不大时，两者效率可以忽略， 但是数组长度变大时，System.arrayCopy()还是有效率优势的， 但是感觉效率提升没有想象的大。