在不覆盖旧数组的情况下更改数组的值

Question

这里我试图将数组顺时针旋转90度，我将 'mat' 的值分配给 'new array'(line:9)。当我试图覆盖 'new array' 的值（第 13 行）时，'mat' 数组的值也被覆盖导致实际值发生变化并在结果上给出错误，建议我进行一些编辑停止覆盖 'mat' 数组

class maxpop {
public static void main(String[] args) {
    Rotation();
}
static void Rotation(){
    int[][] mat = {{0,0,0},{1,1,1},{2,2,2}};
    int[][] newarray = new int[mat.length][mat.length];
    int p;
    newarray=mat;
    for (int i = 0; i < newarray.length; i++) {
        p=mat.length-1;
        for (int j = 0; j <newarray.length; j++,p--) {
            newarray[i][j] = newarray[p][i];
        }
        
    }

    for (int i = 0; i < newarray.length; i++) {
        for (int j = 0; j < newarray.length; j++) {
            System.out.print(newarray[i][j]);
        }
        //p--;
        System.out.println();
    }}}

Answer 1

在此代码中：

int[][] mat = {{0,0,0},{1,1,1},{2,2,2}};   // (A)
int[][] newarray = new int[mat.length][mat.length];   // (B)
int p;
newarray=mat;

行 newarray=mat; 将对旧数组的引用分配给 newarray 变量。您在 (B) 中创建并分配给 newarray 的新数组将无法再访问。 mat 和 newarray 都将指向与 (A) 中声明的相同的数组。您需要删除该行。您还需要从 mat 数组复制。

public class MaxPop {

    public static void main(String[] args) {
        rotation();
    }

    static void rotation() {
        int[][] mat = { { 0, 0, 0 }, { 1, 1, 1 }, { 2, 2, 2 } };
        int[][] newarray = new int[mat.length][mat.length];
        int p;

        for (int i = 0; i < newarray.length; i++) {
            p = mat.length - 1;
            for (int j = 0; j < newarray.length; j++, p--) {
                newarray[i][j] = mat[p][i];
            }

        }

        for (int i = 0; i < newarray.length; i++) {
            for (int j = 0; j < newarray.length; j++) {
                System.out.print(newarray[i][j]);
            }
            System.out.println();
        }
        System.out.println();

        for (int i = 0; i < mat.length; i++) {
            for (int j = 0; j < mat.length; j++) {
                System.out.print(mat[i][j]);
            }
            System.out.println();
        }
    }
}

打印：

210
210
210

000
111
222

Answer 2

当你在做 newarray=mat 时，两个数组都指向同一个对象，改变一个会改变另一个停止覆盖 mat 数组并旋转 90deg

class maxpop {
public static void main(String[] args) {
    Rotation();
}
static void Rotation(){
    int[][] mat = {{0,0,0},{1,1,1},{2,2,2}};
    int[][] newarray = new int[mat.length][mat.length];
    int p;
    int k=0;
 while (k<no of times you want to rotate) {
    for (int i = 0; i < newarray.length; i++) {
        p =mat.length-1;
        for (int j = 0; j <newarray.length; j++,p--) {
            newarray[i][j] = mat[p][i];
            System.out.print(newarray[i][j]);
        } 
        System.out.println();   
    }
   int[][] newarrray_2=new int[newarray.length] 
   [newarray.length];/*everytime the loop runs it will create 
    newobject with 0 
    values, if you don't create a new array each time 
    newarry,newarray_2 
    will 
   point the same object,and newarray will not get initialised to 
   0 later*/
   mat=newarray;//mat will get overwrite 
   newarray=newarrray_2;/*a new 0 value will be initialised to 
    new array*/
   k++;
}
}}

在不覆盖旧数组的情况下更改数组的值

Change value of array without overwriting the old array

java

arrays

multidimensional-array