秒懂数组拷贝，感知新境界

小鱼儿 2021-09-08 09:14 231阅读 0赞

## 一、前言 ##

最近遇到了数组拷贝的问题，之前从来都没想过，数组居然还用拷贝？

小编在今天之前，用的都是循环赋值的方式进行数组拷贝，速度将对较慢，代码看起来很low，不推荐使用。

今天就这个机会，总结一波，分享给大家。

## 二、System.arraycopy与Arrays.copyOf（浅拷贝） ##

这个是System提供的方法，也是我推荐的一种拷贝方式，它是浅拷贝，对非基本类型而言，它拷贝的是对象的引用，而不是去新建一个新的对象，这个方法不是Java写的，底层是用C或C++实现的，速度比较快。

通过源码分析，Arrays.copyOf是一个浅拷贝。

public static byte[] copyOfRange(byte[] original, int from, int to) {                   
       int newLength = to - from;
       if (newLength < 0)
           throw new IllegalArgumentException(from + " > " + to);
           byte[] copy = new byte[newLength];
           System.arraycopy(original, from, copy, 0,
                  Math.min(original.length - from, newLength));
            return copy;
        }

实际上它调用的还是System.arraycopy，所以它也是浅拷贝。

### 1、基本类型数组复制 ###

package com.guor.test.javaSE.collection;
     
    import java.util.Arrays;
     
    import com.guor.test.User;
     
    public class ArrayTest {
     
    	public static void main(String[] args) {
    		beanCopy();
    	}
    	
    	//**************************************************************
    	private static void copySelf() {
    		int[] ids = { 1, 2, 3, 4, 5 };  
    		System.out.println(Arrays.toString(ids));
    		//System.arraycopy(src, srcPos, dest, destPos, length);
    		// 把从索引0开始的2个数字复制到索引为3的位置上  
    		System.arraycopy(ids, 0, ids, 3, 2);
    		System.out.println(Arrays.toString(ids));//[1, 2, 3, 1, 2]
    	}
    	
    	private static void copyToOther() {
    		int[] ids = { 1, 2, 3, 4, 5 };  
    		//将数据的索引1开始的3个数据复制到目标的索引为0的位置上  
    		int[] other = new int[5];
    		System.arraycopy(ids, 1, other, 0, 3);
    		System.out.println(Arrays.toString(ids));//[1, 2, 3, 4, 5]深复制
    		System.out.println(Arrays.toString(other));//[2, 3, 4, 0, 0]
    	}
    }

### 2、Object数组复制 ###

//如果是类型转换问题，获取整形
    private static void getIntegerArrayFromObjectArray() {
        Object[] obj1 = { 1, 2, 3, "4", "5" };
        Integer[] obj2 = new Integer[5];
    
        try {
            System.arraycopy(obj1, 0, obj2, 0, obj1.length);
        } catch (Exception e) {
            System.out.println("transfer exception:"+e);
        }
        System.out.println(Arrays.toString(obj1));
        System.out.println(Arrays.toString(obj2));
    }
    
    //获取Object数组中的字符串类型数据
    private static void getStringArrayFromObjectArray1() {
        Object[] obj3 = { 1, 2, 3, "4", "5" };
        String[] obj4 = new String[5];
        try {
            System.arraycopy(obj3, 2, obj4, 2, 3);
        } catch (Exception e) {
            //transfer exception:java.lang.ArrayStoreException
            System.out.println("transfer exception:"+e);
        }
        System.out.println(Arrays.toString(obj3));
        //[null, null, null, null, null]
        System.out.println(Arrays.toString(obj4));
    }
    
    //获取Object数组中的字符串类型数据
    private static void getStringArrayFromObjectArray2() {
        Object[] obj3 = { 1, 2, 3, "4", "5" };
        String[] obj4 = new String[5];
        try {
            System.arraycopy(obj3, 3, obj4, 3, 2);
        } catch (Exception e) {
            System.out.println("transfer exception:"+e);
        }
        System.out.println(Arrays.toString(obj3));
        //[null, null, null, 4, 5]
        System.out.println(Arrays.toString(obj4));
        obj3[3] = "zhangssan";
        System.out.println("查看是浅复制还是深复制~~~~~");
        System.out.println(Arrays.toString(obj3));
        System.out.println(Arrays.toString(obj4));
    }

### 3、多维数组复制 ###

//多维数组
    public static void twoArray() {
        int[] arr1 = {1, 2};
        int[] arr2 = {3, 4};
        int[] arr3 = {5, 6};
    
        int[][] src = new int[][]{arr1, arr2, arr3};
    
        print("原始模样：", src);
        int[][] dest = new int[3][];
        System.arraycopy(src, 0, dest, 0, 3);
    
        System.out.println("改变前");
        print("src = ", src);
        print("dest = ", dest);
    
        //原数组改变后观察新数组是否改变，改变->浅复制，不改变->深复制
        src[0][0] = -1;
    
        System.out.println("改变后");
        print("src = ", src);
        print("dest = ", dest);
    }

### 4、对象数组复制 ###

//对象复制
    private static void beanCopy() {
        User user1 = new User("zs",18);
        User user2 = new User("ls",18);
        User user3 = new User("ww",18);
        User[] userArraySrc = {user1, user2, user3};
        User[] userArrayDest = new User[3];
        System.out.println("对象复制，原始模样："+Arrays.toString(userArraySrc));
        System.arraycopy(userArraySrc, 0, userArrayDest, 0, userArraySrc.length);
        System.out.println("userArrayDest," + Arrays.toString(userArrayDest));
        System.out.println("------------改变原对象------------------");
        userArraySrc[0] = new User("su",20);
        System.out.println("***" + Arrays.toString(userArraySrc));
        System.out.println("***" + Arrays.toString(userArrayDest));
    }
    
    //二维数组toString()
    private static void print(String string, int[][] arr) {
        System.out.print(string);
        for (int[] a : arr) {
            for (int i : a) {
                System.out.print(i + " ");
            }
            System.out.print(",");
        }
        System.out.println();
    }

## 三、clone() ##

protected native Object clone() throws CloneNotSupportedException;

clone()也是native方法，所以也是C语言实现的。

### 1、基本数组类型clone() ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d1b3J1aV9qYXZh_size_16_color_FFFFFF_t_70][]

### 2、对象数组clone() ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d1b3J1aV9qYXZh_size_16_color_FFFFFF_t_70 1][]

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[Java]: https://blog.csdn.net/guorui_java/article/details/112391105
[Spring]: https://blog.csdn.net/guorui_java/article/details/104018528
[springBoot]: https://blog.csdn.net/guorui_java/article/details/104137262
[Link 1]: https://blog.csdn.net/guorui_java/article/details/106217472
[Java_23]: https://blog.csdn.net/guorui_java/article/details/104026988
[Java 1]: https://blog.csdn.net/guorui_java/article/details/107803283
[Linux]: https://blog.csdn.net/guorui_java/article/details/117430091
[Redis]: https://blog.csdn.net/guorui_java/article/details/116850879