如何检查数组是否是二维数组中的元素之一

Question

I am trying to assert that an array of string elements is one of the elements of a 2-dimensional array using the standard Collection.isIn matcher provided with Hamcrest library. Unfortunately receiving the following assertion exception:

java.lang.AssertionError: 
Expected: one of {["A", "B", "C"], ["A", "B", "C"]}
   but: was ["A", "B", "C"]

Code:

String[][] expected = new String[][] { { "A", "B", "C" }, { "A", "B", "C" } };
String[] actual = new String[] { "A", "B", "C" };

assertThat(actual, isIn(expected));

Can I validate using hamcrest in such a manner? Or do I need to create my own matcher for the given scenario?

Answer 1

The issue is that Object.equals() doesn't do what you might expect when the objects are arrays. As you probably already know, you have to use Arrays.equals() -- but Hamcrest isIn() does not allow for this.

Probably the simplest solution is to convert to List even if only for the test -- because List.equals() works as Hamcrest expects:

...
import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.collection.IsIn.in;
...

String[][] expected = new String[][] { { "A", "B", "C" }, { "A", "B", "C" } };

Object[] expectedLists = Arrays.stream(expected).map(Arrays::asList).toArray();

String[] actual = new String[] { "A", "B", "C" };

assertThat(Arrays.asList(actual), is(in(expectedLists)));

Answer 2

您的数组可能包含与expected的数组相同的内容，但它不是同一个对象。

Answer 3

First of all, you would be better off using List<> instead of arrays.

Secondly, yes, if you insist on using arrays, you will need to write your own 'array-contains-element' function. You can implement this function using a loop over the major dimension of the array, invoking the Arrays.equals() method to compare the contents of two one-dimensional arrays.

Answer 4

I'm guessing the issue is because the method compares objects, and not contents. Basically, even though both have the same content, they are not the same object. See here in the docs

Do this instead:

String[] actual = new String[]{"A1 C1 E1 F1 J1", "A1 C1 E1 F1 K1", "A1 B1 G1 H1"}; String[][] expected = new String[][]{actual, {"A1 C1 E1 F1 J1", "A1 C1 E1 F1 K1", "A1 B1 G1 H1"}};

Answer 5

The problem with collection.IsIn in your context, is that your elements of your list is an array and it will use the Array#equals to compare each element.

More specifically

// It will print false, because Array.equals check the reference 
// of objects, not the content
System.out.println(actual.equals(new String[]{"A1 C1 E1 F1 J1", "A1 C1 E1 F1 K1", "A1 B1 G1 H1"}));

So I suggest creating a custom matcher that uses Arrays.equals from java. It will compare the content of arrays for you. Something like code below:

public boolean matches(Object item) {
    final String[] actualStringArray = (String [])item;

    List<String[]> listOfStringArrays = Arrays.asList(expectedStringMatrix);

    for (String[] stringArray : listOfStringArrays) {
        // Arrays.equals to compare the contents of two array!
        if (Arrays.equals(stringArray, actualStringArray)) {
            return true;
        }
    }
    return false;
}