This can be rewritten as follows: What methods are there to copy a Java array?

Preface

The so-called copying an array refers to copying the elements in one array in another array

There are the following 4 methods to implement array copying in Java:

• Original assignment method

• The copyOf() method of the Arrays class

• The copyOfRange() of the Arrays class Method

• arraycopy() method of System class

• clone() method of Object class

1. Original assignment method

public static void method01(int[] arr, int[] ans) {
		for (int i = 0; i < arr.length; i++) {
			ans[i] = arr[i];
		}
		System.out.println("复制的ans数组为 " + Arrays.toString(ans));
	}

2. Use the copyOf() method

The copyOf() method is to copy the array to the specified length

The copyOf() method of the Arrays class The syntax format is as follows:

Arrays.copyOf(dataType[] srcArray,int length);

Among them, srcArray represents the array to be copied, and length represents the length of the new array after copying.

When using this method to copy an array, copying starts from the first element of the original array (index value is 0) by default, and the length of the target array will be length. If length is greater than srcArray.length, the target array will be filled with the default value; if length is less than srcArray.length, it will be copied until the length element (index value is length-1).

Note: If the target array already exists, it will be reconstructed.

public static void method02(int[] arr, int[] ans) {
		ans = Arrays.copyOf(arr, arr.length + 3);
		System.out.println("复制的ans数组为 " + Arrays.toString(ans));
	}

3. Use the CopyOfRange() method

The CopyOfRange() method of the Arrays class is another method of copying an array. Its syntax is as follows:

Arrays.copyOfRange(dataType[] srcArray,int startIndex,int endIndex)

Where:

• #srcArray represents the original array.

• startIndex indicates the starting index to start copying. The target array will contain the element corresponding to the starting index. In addition, startIndex must be between 0 and srcArray.length.

• endIndex represents the termination index. The target array will not contain the element corresponding to the termination index. endIndex must be greater than or equal to startIndex, and can be greater than srcArray.length. If it is greater than srcArray.length, the target array Fill in with default values.

Note: If the target array already exists, it will be reconstructed.

public static void method03(int[] arr, int[] ans) {
		ans = Arrays.copyOfRange(arr, 0, arr.length + 3);
		System.out.println("复制的ans数组为 " + Arrays.toString(ans));
	}

4. Use the arraycopy() method

arraycopy() method is located in the java.lang.System class, and its syntax is as follows:

System.arraycopy(dataType[] srcArray,int srcIndex,int destArray,int destIndex,int length)

Among them, srcArray represents the original array; srcIndex represents the starting index in the original array; destArray represents the target array; destIndex represents the starting index in the target array; length represents the length of the array to be copied.

When using this method to copy an array, length srcIndex must be less than or equal to srcArray.length, and length destIndex must be less than or equal to destArray.length.

Note: The target array must already exist and will not be reconstructed, which is equivalent to replacing some elements in the target array.

public static void method03(int[] arr, int[] ans) {
		ans = Arrays.copyOfRange(arr, 0, arr.length + 3);
		System.out.println("复制的ans数组为 " + Arrays.toString(ans));
	}

5. Use the clone() method

The clone() method can also copy an array. This method is a method in class Object and can create an object with a separate memory space. Because the array is also an Object class, you can also use the clone() method of the array object to copy the array.

The return value of the clone() method is of type Object, which needs to be cast to the appropriate type. Its syntax is relatively simple:

array_name.clone()

public static void method05(int[] arr, int[] ans) {
		ans = arr.clone();
		System.out.println("复制的ans数组为 " + Arrays.toString(ans));
	}

Note: The above methods are all shallow copies. Shallow copy only copies the reference address of the object. The two objects point to the same memory address, so if any value is modified, the other value will change accordingly. Deep copy copies objects and values. If any value of the two objects is modified, the other value will not change.

Complete test case

package com.zhuang;

import java.util.Arrays;

/**
 * 
 * @ClassName: ArrayCopy
 * @Description:测试数组复制的几种方法
 * @author: KangXiaoZhuang
 * @date: 2022年10月8日 下午2:19:06
 */
public class ArrayCopy {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int[] arr = new int[] { 57, 81, 68, 75, 91 };
		int[] ans = new int[arr.length];
		method01(arr, ans);
		method02(arr, ans);
		method03(arr, ans);
		method04(arr, ans);
		method05(arr, ans);
	}

	/**
	 * 
	 * @Title: method01
	 * @Description: 原始复制方法
	 * @author: KangXiaoZhuang
	 * @param: @param arr 原始数组
	 * @param: @param ans 目标数组
	 * @return: void
	 * @throws
	 */
	public static void method01(int[] arr, int[] ans) {
		for (int i = 0; i < arr.length; i++) {
			ans[i] = arr[i];
		}
		System.out.println("原始复制方法复制的ans数组为 " + Arrays.toString(ans));
	}

	/**
	 * 
	 * @Title: method02
	 * @Description: copyOf()方法
	 * @author: KangXiaoZhuang
	 * @param: @param arr 原始数组
	 * @param: @param ans 目标数组
	 * @return: void
	 * @throws
	 */
	public static void method02(int[] arr, int[] ans) {
		ans = Arrays.copyOf(arr, arr.length + 3);
		System.out.println("copyOf()方法复制的ans数组为 " + Arrays.toString(ans));
	}

	/**
	 * 
	 * @Title: method03
	 * @Description: copyOfRange()方法
	 * @author: KangXiaoZhuang
	 * @param: @param arr 原始数组
	 * @param: @param ans 目标数组
	 * @return: void
	 * @throws
	 */
	public static void method03(int[] arr, int[] ans) {
		ans = Arrays.copyOfRange(arr, 0, arr.length + 3);
		System.out.println("copyOfRange()方法复制的ans数组为 " + Arrays.toString(ans));
	}
	
	/**
	 * 
	 * @Title: method04   
	 * @Description: arraycopy()方法
	 * @author: KangXiaoZhuang   
	 * @param: @param arr 原始数组
	 * @param: @param ans 目标数组    
	 * @return: void      
	 * @throws
	 */
	public static void method04(int[] arr, int[] ans) {
		System.arraycopy(arr, 0, ans, 0, 5);
		System.out.println("arraycopy()方法复制的ans数组为 " + Arrays.toString(ans));
	}
	
	/**
	 * 
	 * @Title: method05   
	 * @Description: 使用clone()方法
	 * @author: KangXiaoZhuang   
	 * @param: @param arr
	 * @param: @param ans      
	 * @return: void      
	 * @throws
	 */
	public static void method05(int[] arr, int[] ans) {
		ans = arr.clone();
		System.out.println("clone()方法复制的ans数组为 " + Arrays.toString(ans));
	}
}

Output

The ans array copied by the original copy method is [ 57, 81, 68, 75, 91]
The ans array copied by the copyOf() method is [57, 81, 68, 75, 91, 0, 0, 0]
The ans array copied by the copyOfRange() method The ans array copied for [57, 81, 68, 75, 91, 0, 0, 0]
arraycopy() method is copied for [57, 81, 68, 75, 91]
clone() method The ans array is [57, 81, 68, 75, 91]

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