Почему мой код изменяет неправильный массив?

Question

Это мой класс с моими методами

public class Matrix { 
    //this is the stored matrix given from another class 
    private double[][] stored; 

    //constructor 
    public Matrix(double[][] input){ 
    stored = input; 
    } 

    public double[] getRow(int rownum){ 
    return stored[rownum]; 
    } 

    //change current matrix by swapping rows rowA and rowB 
    public void swap(int rowA, int rowB){ 
    double[] temp = stored[rowA]; 
    stored[rowA] = stored[rowB]; 
    stored[rowB] = temp; 
    } 

    // looking only at column column_num in matrix, 
    // return index of which row has largest value 
    public int maxRow(int column_num){ 
    double largest = 0.0; //current largest value 
    int index = 0; //index of row with largest value 
    for(int i = 0; i < stored.length; i++){ 
     if(stored[i][column_num] > largest){ 
     largest = stored[i][column_num]; 
     index = i; 
     } 
    } 
    return index; 
    } 

    //method to iterate through a row and scale by factor 
    public void scaleRow(int rownum, double factor){ 
    for(int i = 0; i < stored[rownum].length; i++){ 
     double cValue = stored[rownum][i]; 
     stored[rownum][i] = cValue*factor; 
    } 
    } 

} 

Это мой тестовый класс

import java.util.Arrays; 
public class MatrixTest { 
    public static void main(String[] args) { 
    /* test cases for Matrix class methods */ 
    double[][] matrixA = {{1,2,3,4},{2,4,6,8},{9,10,11,12}}; 
    double[][] matrixB = {{0.92,-900,44},{1201,18.264,-21.0},{0,0,0}}; 
    double[][] matrixC = {{1.5E-12,-6.034E2},{41.8,-125E-3}}; 
    Matrix One = new Matrix(matrixA); 
    Matrix Two = new Matrix(matrixB); 
    Matrix Three = new Matrix(matrixC); 

    /* test whether or not maxRow works properly */ 
    if (One.maxRow(0) == 2) { 
      System.out.println("Passed maxRow test for matrix One"); } 
    else { System.out.println("Failed maxRow test for matrix One"); } 
    if (Two.maxRow(1) == 1) { 
      System.out.println("Passed maxRow test for matrix Two"); } 
    else { System.out.println("Failed maxRow test for matrix Two"); } 

    /* test whether or not scaleRow works properly */ 
    One.scaleRow(0,2.0); // scale row 0 by 2.0 
    if (Arrays.equals(One.getRow(0),matrixA[1])) { 
      System.out.println("Passed scaleRow test for matrix One"); } 
    else { System.out.println("Failed scaleRow test for matrix One"); } 
    Two.scaleRow(2,12.608); // scale row 2 by 12.608 
    if (Arrays.equals(Two.getRow(2),matrixB[2])) { 
      System.out.println("Passed scaleRow test for matrix Two"); } 
    else { System.out.println("Failed scaleRow test for matrix Two"); } 
    One.scaleRow(0,0.5); // scale row 0 by 0.5 
    if (Arrays.equals(One.getRow(0),matrixA[0])) { 
      System.out.println("Passed scaleRow test for matrix Three"); } 
    else { System.out.println("Failed scaleRow test for matrix Three"); } 

    for(int i = 0; i < matrixA[2].length; i++){ 
     System.out.println(matrixA[2][i]); 
    } 
    System.out.println("This prints row 2 of matrixA before the swap"); 

    /* test whether or not swap method works properly */ 
    One.swap(2,0); // swap contents of Row 2 with Row 0 
    if (Arrays.equals(One.getRow(0),matrixA[2]) && 
     Arrays.equals(One.getRow(2),matrixA[0])) { 
      System.out.println("Passed swap test for matrix One"); } 
    else { 
     double[] row0 = One.getRow(0); 
     for(int i = 0; i < row0.length; i++){ 
      System.out.println(row0[i]); 
     } 
     System.out.println("This prints row 0 of One after the swap"); 
     for(int i = 0; i < row0.length; i++){ 
      System.out.println(matrixA[2][i]); 
     } 
     System.out.println("This prints row 2 of matrixA after the swap"); 
     System.out.println("Failed swap test for matrix One"); 
    } 
    Two.swap(0,1); Two.swap(1,2); Two.swap(1,0); // fancy swap sequence 
    if (Arrays.equals(Two.getRow(0),matrixB[2]) && 
     Arrays.equals(Two.getRow(2),matrixB[0])) { 
      System.out.println("Passed swap test for matrix Two"); } 
    else { System.out.println("Failed swap test for matrix Two"); } 

    } 
    } 

Это мой выход

Passed maxRow test for matrix One 
Passed maxRow test for matrix Two 
Passed scaleRow test for matrix One 
Passed scaleRow test for matrix Two 
Passed scaleRow test for matrix Three 
9.0 
10.0 
11.0 
12.0 
This prints row 2 of matrixA before the swap 
9.0 
10.0 
11.0 
12.0 
This prints row 0 of One after the swap 
1.0 
2.0 
3.0 
4.0 
This prints row 2 of matrixA after the swap 
Failed swap test for matrix One 
Failed swap test for matrix Two 

Почему матрица А модифицируется после того, как я выполнить обмен на Один?

* Примечание. Это печатает строку вниз, потому что я не хочу делать все форматирование печати.

Answer 1

Вашего Матрица конструктор просто копирует ссылки на массив:

public Matrix(double[][] input){ 
    stored = input; 
} 

Поэтому как matrixA и массив, содержащийся в One объекте один и тот же массив.

Если вы не хотите, чтобы ваши Matrix экземпляров, чтобы изменить исходный входной массив, вы должны создать копию массивы:

public Matrix(double[][] input){ 
    // stored = Arrays.copyOf(input,input.length); // this would only work for 1D arrays 
    stored = new double[input.length][]; 
    for (int i = 0; i < input.length; i++) 
     stored[i] = Arrays.copyOf(input[i],input[i].length); 
}