使用 ,equals() 比较对象时出现意外的断言失败错误答案

【问题标题】：Unexpected assertion failed error when comparing objects using ,equals()使用 ,equals() 比较对象时出现意外的断言失败错误
【发布时间】：2018-07-27 19:02:01
【问题描述】：

当我使用添加矩阵的 add 方法比较具有相同值的 2 个对象时，为什么会出现断言失败错误。下面是我的 add 方法（来自 AbstractMatrix）：

public abstract class AbstractMatrix implements Matrix{

private static MatrixFactory factory = new DefaultMatrixFactory();
private Matrix getNewMatrixInstance(Matrix kind,int numberOfRows, int numberOfColumns)throws MatrixException{
    return factory.getInstance(kind.getClass(), numberOfRows, numberOfColumns);
}
public static void setFactory(MatrixFactory aFactory){factory = aFactory;}

public final boolean isSameSize(final Matrix m){
    return (getNumberOfRows() == m.getNumberOfRows()) && (getNumberOfColumns() == m.getNumberOfColumns());
}

public final Matrix add(final Matrix m) throws MatrixException{
    if (!isSameSize(m)){
        throw new MatrixException("Trying to add matrices of different sizes");
    }
    final Matrix result = getNewMatrixInstance(this, getNumberOfRows(), getNumberOfColumns());

    for (int row = 0; row < getNumberOfRows(); row++){
        for (int column = 0; column < getNumberOfColumns(); column++){
            final double value = getElement(row, column) + m.getElement(row, column);
            result.setElement(row, column, value);
        }
    }
    return result;
}

这是我的 JUnit 测试：

@Test
void testAdd() throws MatrixException {
    Matrix m1 = factory.getInstance(ArrayMatrix.class,new double[][]{{0,0},{0,0}});
    Matrix m2 = factory.getInstance(ArrayMatrix.class,new double[][]{{0,0},{0,0}});
    Matrix m3 = m1.add(m2);
    Matrix m4 = factory.getInstance(ArrayMatrix.class,new double[][]{{0,0},{0,0}});
    assertEquals(true, m3.equals(m4));
}

显然 m3 是与 m4 相同的矩阵，但我得到一个 AssertionFailedError 告诉我它是错误的。

其他类：

public class ArrayMatrix extends AbstractMatrix{

    private double[][] elements;

    public ArrayMatrix(final int rows, final int columns) throws MatrixException{
     // Initialise a new matrix with all the elements set to 0.0
        if (rows < 0 || columns < 0) {
            throw new MatrixException("Negative rows or columns are not allowed");
        }
        this.elements = new double[rows][columns];
        int i,j;
        for (i=0;i<rows;i++) {
            for (j=0;j<columns;j++) {
                elements[i][j]= 0.0;             
            }        
        }
    }
    public ArrayMatrix(double[][] content) throws MatrixException{
 // Initialise a new matrix storing the data provided by the
 // double[][] parameter.

        int rows = content.length;
        int columns = content[0].length;
        elements = new double[rows][columns];
        int i,j;
        for (i=0;i<rows;i++) {
            for(j=0;j<columns;j++) {
                elements[i][j] = content[i][j];
            }
        }      
    }

    public int getNumberOfRows(){
 // Number of rows in matrix
        int noRows = elements.length;
        return noRows;
    }

    public int getNumberOfColumns(){
 // Number of columns in matrix
        int noColumns = elements[0].length;
        return noColumns;
    }

    public double getElement(final int row, final int column) throws MatrixException{
         // Return the element at the specified position or throw an exception
        if (elements.length<=row) {
            throw new MatrixException("Attempt to access invalid element ("+row+","+column+")");
        }
        if (elements[0].length<column){
            throw new MatrixException("Attempt to access invalid element ("+row+","+column+")");
        }
        else {return elements[row][column];}
    }

    public void setElement(final int row, final int column, final double value) throws MatrixException{
         // Set the element at the specified position or throw an exception
        if (elements.length<=row) {
             throw new MatrixException("Attempt to access invalid element ("+row+","+column+")");}
        if (elements[0].length<column){
             throw new MatrixException("Attempt to access invalid element ("+row+","+column+")");}
        else {elements[row][column] = value;}
    }
}

界面：

public interface Matrix {
    public int getNumberOfRows();
    public int getNumberOfColumns();
    public double getElement(final int row, final int column)throws MatrixException;
    public void setElement(final int row, final int column, final double value)throws MatrixException;
    public Matrix add(final Matrix m) throws MatrixException;
    public Matrix subtract(final Matrix m) throws MatrixException;
    public Matrix multiply(final Matrix m) throws MatrixException;
}

【问题讨论】：

你为什么使用 assertEquals(, ) 而不是 assertEquals(m3, m4)？
@K.Dackow 那也行不通。我收到此错误：imgur.com/a/UWfmZlC
请编辑您的问题并将您的代码发布为minimal reproducible example。不要在其他网站上发布指向代码图像、错误图像或代码的链接。当这些链接失效时，您的问题毫无意义。从 10 个不同的页面中抓取您的问题的信息也是一种痛苦。让他人轻松帮助您。
@Robert 注意，只是不想用代码堵塞整个页面，
这就是人们要求最小示例的原因

标签： java object multidimensional-array junit

【解决方案1】：

查看您发布的文档，ArrayMatrix 类似乎没有覆盖 .equals() 方法。默认.equals 比较基于location in memory 的对象，因此您发布的屏幕截图中出现错误。

要解决此问题，您可以使用write your own .equals() 方法来根据数组内部的内容来比较数组！

【讨论】：