Java中数组复制的几种方式以及数组合并

1.Object.clone()

简单直接，只能对源数组完整地复制

2.Arrays.copyOf(T[] original, int newLength)

可以只复制源数组中部分元素，但复制的起始位置固定为0

3.Arrays.copyOfRange(T[] original, int from, int to)

可以指定复制的起始位置

4.System.arraycopy(Object src, int srcPos, Object dest, int destPos, int length)

复杂，但可以将源数组中的部分元素复制到目标数组的指定位置（此方法最灵活，可实现上述1、2、3的功能）

1、2、3都具有一定的局限性（返回一个新的数组，无法将源数组中的元素复制到已存在的数组中），

故合并数组的操作只能通过System.arraycopy来完成，以下为示例：

JApp.java

import static java.lang.System.out;
import java.lang.reflect.Array;
 
public class JApp {
 
    //没有使用Java中预定义的函数
//    private static int[] mergeArrays(int[]... arrays) {
//        int lengthOfNewArray = 0;
//        for (int i = 0; i < arrays.length; ++i) {
//            lengthOfNewArray += arrays[i].length;
//        }
//        int[] newArray = new int[lengthOfNewArray];
//        int index = 0;
//        for (int[] array : arrays) {
//            for (int i : array) {
//                newArray[index++] = i;
//            }
//        }
//        return newArray;
//    }
    private static <T> T[] mergeArrays(T[]... arrays) {
        int lengthOfNewArray = 0;
        for (int i = 0; i < arrays.length; ++i) {
            lengthOfNewArray += arrays[i].length;
        }
        //使用(T[])Array.newInstance(...)可避免(T[])new Object[...]引发的ClassCastException
        T[] newArray = (T[]) Array.newInstance(arrays[0].getClass().getComponentType(), lengthOfNewArray);
        int destPos = 0;
        for (int i = 0; i < arrays.length; ++i) {
            System.arraycopy(arrays[i], 0, newArray, destPos, arrays[i].length);
            destPos += arrays[i].length;
        }
        return newArray;
    }
 
    private static int[] mergeArrays(int[]... arrays) {
        int lengthOfNewArray = 0;
        for (int i = 0; i < arrays.length; ++i) {
            lengthOfNewArray += arrays[i].length;
        }
        int[] newArray = new int[lengthOfNewArray];
        int destPos = 0;
        for (int i = 0; i < arrays.length; ++i) {
            System.arraycopy(arrays[i], 0, newArray, destPos, arrays[i].length);
            destPos += arrays[i].length;
        }
        return newArray;
    }
 
    public static void main(String[] args) {
        int[] ints1 = {0, 1, 2, 3, 4};
        int[] ints2 = {5, 6, 7, 8, 9};
        int[] ints3 = {10, 11, 12, 13, 14};
        int[] buffer = new int[ints1.length + ints2.length + ints3.length];
        for (int i : buffer) {
            out.print(i + "  ");
        }
        out.println();
        System.arraycopy(ints1, 0, buffer, 0, ints1.length);
        System.arraycopy(ints2, 0, buffer, ints1.length, ints2.length);
        System.arraycopy(ints3, 0, buffer, ints1.length + ints2.length, ints3.length);
        for (int i : buffer) {
            out.print(i + "  ");
        }
        out.println();
        int[] array = mergeArrays(ints1, ints2, ints3);
        for (int i : array) {
            out.print(i + "  ");
        }
        out.println();
        Object[] objects = mergeArrays(new Object[]{"a", "b", "c"}, new Object[]{"D", "E"}, new Object[]{"测试", "Bu Ish", "布衣食"});
        for (Object o : objects) {
            out.print(o + "、");
        }
        out.println();
        String[] strings = mergeArrays(new String[]{"a", "b", "c"}, new String[]{"D", "E"}, new String[]{"测试", "Bu Ish", "布衣食"});
        for (String s : strings) {
            out.print(s + "、");
        }
        out.println();
    }
}