为什么该方法会更改输入参数（数组），尽管我将它复制到方法中？

Question

我是 Java 新手。我有一个方法应该返回一个新的修改数组。但是在执行代码之后，作为参数的数组也发生了变化。请解释我在哪里修改原始数组。如何解决这个问题？我很绝望，因为我不明白我在哪里传递链接而不是值。

import java.util.Arrays;

public class question {

    public static void main(String[] args) {

        final int[][] inputArray = new int[][]{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
        System.out.println("Original array:");
        System.out.println(Arrays.deepToString(inputArray));
        //Display
        //[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

        System.out.println("Array after delete line:");
        System.out.println(Arrays.deepToString((removeLine(1, inputArray))));
        //Display - ok
        //[[1, 2, 3], [7, 8, 9], [0, 0, 0]]


        System.out.println("The original array after using in method:");
        System.out.println(Arrays.deepToString(inputArray));
        //Display
        //[[1, 2, 3], [4, 5, 6], [0, 0, 0]]
        //I don't understand this.
    }

    static int[][] removeLine(int k, int[][] inpArray) {

        //I copy in resultArray to keep unchanged inpArray.
        int[][] resultArray = new int[inpArray.length][inpArray[0].length];
        System.arraycopy(inpArray, 0, resultArray, 0, inpArray.length);

        //I change resultArray.
        for (int i = k; i < resultArray.length - 1; i++) {
            resultArray[i] = Arrays.copyOf(resultArray[i + 1], resultArray[i + 1].length);
        }
        Arrays.fill(resultArray[resultArray.length - 1], 0);

        //I return resultArray.
        return resultArray;
    }
}

Answer 1

System.arraycopy 不做深拷贝；而是做一个浅拷贝。换句话说，它复制了引用，因此System.arraycopy(inpArray, 0, resultArray, 0, inpArray.length); 的行为如下：

inpArray[0] and resultArray[0] refer to the same object
inpArray[1] and resultArray[1] refer to the same object
inpArray[2] and resultArray[2] refer to the same object

等等……

这也意味着

inpArray[0] == resultArray[0] is true
inpArray[1] == resultArray[1] is true
inpArray[2] == resultArray[2] is true

等等……

Answer 2

变化：

//I copy in resultArray to keep unchanged inpArray.
int[][] resultArray = new int[inpArray.length][inpArray[0].length];
System.arraycopy(inpArray, 0, resultArray, 0, inpArray.length);

到：

// I copy in resultArray to keep unchanged inpArray.
int[][] resultArray = new int[inpArray.length][];
for (int i = 0; i < inpArray.length; i++) {
    resultArray[i] = new int[inpArray[i].length];

    for (int j = 0; j < resultArray[i].length; j++)
        resultArray[i][j] = inpArray[i][j];
}

除了您没有创建该区域的实际副本这一事实之外，您还将resultArray 的每个子数组设置为inpArray 中第一个元素的长度。大多数数组都会有不同长度的子数组，所以你应该给每个子数组一个单独的长度。