[java] How do I assert equality on two classes without an equals method?

Say I have a class with no equals() method, to which do not have the source. I want to assert equality on two instances of that class.

I can do multiple asserts:

assertEquals(obj1.getFieldA(), obj2.getFieldA());
assertEquals(obj1.getFieldB(), obj2.getFieldB());
assertEquals(obj1.getFieldC(), obj2.getFieldC());
...

I don't like this solution because I don't get the full equality picture if an early assert fails.

I can manually compare on my own and track the result:

String errorStr = "";
if(!obj1.getFieldA().equals(obj2.getFieldA())) {
    errorStr += "expected: " + obj1.getFieldA() + ", actual: " + obj2.getFieldA() + "\n";
}
if(!obj1.getFieldB().equals(obj2.getFieldB())) {
    errorStr += "expected: " + obj1.getFieldB() + ", actual: " + obj2.getFieldB() + "\n";
}
...
assertEquals("", errorStr);

This gives me the full equality picture, but is clunky (and I haven't even accounted for possible null problems). A third option is to use Comparator, but compareTo() will not tell me which fields failed equality.

Is there a better practice to get what I want from the object, without subclassing and overridding equals (ugh)?

I tried all the answers and nothing really worked for me.

So I've created my own method that compares simple java objects without going deep into nested structures...

Method returns null if all fields match or string containing mismatch details.

Only properties that have a getter method are compared.

How to use

        assertNull(TestUtils.diff(obj1,obj2,ignore_field1, ignore_field2));

Sample output if there is a mismatch

Output shows property names and respective values of compared objects

alert_id(1:2), city(Moscow:London)

Code (Java 8 and above):

 public static String diff(Object x1, Object x2, String ... ignored) throws Exception{
        final StringBuilder response = new StringBuilder();
        for (Method m:Arrays.stream(x1.getClass().getMethods()).filter(m->m.getName().startsWith("get")
        && m.getParameterCount()==0).collect(toList())){

            final String field = m.getName().substring(3).toLowerCase();
            if (Arrays.stream(ignored).map(x->x.toLowerCase()).noneMatch(ignoredField->ignoredField.equals(field))){
                Object v1 = m.invoke(x1);
                Object v2 = m.invoke(x2);
                if ( (v1!=null && !v1.equals(v2)) || (v2!=null && !v2.equals(v1))){
                    response.append(field).append("(").append(v1).append(":").append(v2).append(")").append(", ");
                }
            }
        }
        return response.length()==0?null:response.substring(0,response.length()-2);
    }

I had the exact same conundrum when unit testing an Android app, and the easiest solution I came up with was simply to use Gson to convert my actual and expected value objects into json and compare them as strings.

String actual = new Gson().toJson( myObj.getValues() );
String expected = new Gson().toJson( new MyValues(true,1) );

assertEquals(expected, actual);

The advantages of this over manually comparing field-by-field is that you compare all your fields, so even if you later on add a new field to your class it will get automatically tested, as compared to if you were using a bunch of assertEquals() on all the fields, which would then need to be updated if you add more fields to your class.

jUnit also displays the strings for you so you can directly see where they differ. Not sure how reliable the field ordering by Gson is though, that could be a potential problem.

I stumbled on a very similar case.

I wanted to compare on a test that an object had the same attribute values as another one, but methods like is(), refEq(), etc wouldn't work for reasons like my object having a null value in its id attribute.

So this was the solution I found (well, a coworker found):

import static org.apache.commons.lang.builder.CompareToBuilder.reflectionCompare;

assertThat(reflectionCompare(expectedObject, actualObject, new String[]{"fields","to","be","excluded"}), is(0));

If the value obtained from reflectionCompare is 0, it means they are equal. If it is -1 or 1, they differ on some attribute.

Some of the reflection compare methods are shallow

Another option is to convert the object to a json and compare the strings.

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;    
public static String getJsonString(Object obj) {
 try {
    ObjectMapper objectMapper = new ObjectMapper();
    return bjectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(obj);
     } catch (JsonProcessingException e) {
        LOGGER.error("Error parsing log entry", e);
        return null;
    }
}
...
assertEquals(getJsonString(MyexpectedObject), getJsonString(MyActualObject))

Compare field-by-field:

assertNotNull("Object 1 is null", obj1);
assertNotNull("Object 2 is null", obj2);
assertEquals("Field A differs", obj1.getFieldA(), obj2.getFieldA());
assertEquals("Field B differs", obj1.getFieldB(), obj2.getFieldB());
...
assertEquals("Objects are not equal.", obj1, obj2);

You can use reflection to "automate" the full equality testing. you can implement the equality "tracking" code you wrote for a single field, then use reflection to run that test on all fields in the object.

I know it's a bit old, but I hope it helps.

I run into the same problem that you, so, after investigation, I found few similar questions than this one, and, after finding the solution, I'm answering the same in those, since I thought it could to help others.

The most voted answer (not the one picked by the author) of this similar question, is the most suitable solution for you.

Basically, it consist on using the library called Unitils.

This is the use:

User user1 = new User(1, "John", "Doe");
User user2 = new User(1, "John", "Doe");
assertReflectionEquals(user1, user2);

Which will pass even if the class User doesn't implement equals(). You can see more examples and a really cool assert called assertLenientEquals in their tutorial.

This is a generic compare method , that compares two objects of a same class for its values of it fields(keep in mind those are accessible by get method)

public static <T> void compare(T a, T b) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
    AssertionError error = null;
    Class A = a.getClass();
    Class B = a.getClass();
    for (Method mA : A.getDeclaredMethods()) {
        if (mA.getName().startsWith("get")) {
            Method mB = B.getMethod(mA.getName(),null );
            try {
                Assert.assertEquals("Not Matched = ",mA.invoke(a),mB.invoke(b));
            }catch (AssertionError e){
                if(error==null){
                    error = new AssertionError(e);
                }
                else {
                    error.addSuppressed(e);
                }
            }
        }
    }
    if(error!=null){
        throw error ;
    }
}

The library Hamcrest 1.3 Utility Matchers has a special matcher that uses reflection instead of equals.

assertThat(obj1, reflectEquals(obj2));

I generally implement this usecase using org.apache.commons.lang3.builder.EqualsBuilder

Assert.assertTrue(EqualsBuilder.reflectionEquals(expected,actual));

Since this question is old, I will suggest another modern approach using JUnit 5.

I don't like this solution because I don't get the full equality picture if an early assert fails.

With JUnit 5, there is a method called Assertions.assertAll() which will allow you to group all assertions in your test together and it will execute each one and output any failed assertions at the end. This means that any assertions that fail first will not stop the execution of latter assertions.

assertAll("Test obj1 with obj2 equality",
    () -> assertEquals(obj1.getFieldA(), obj2.getFieldA()),
    () -> assertEquals(obj1.getFieldB(), obj2.getFieldB()),
    () -> assertEquals(obj1.getFieldC(), obj2.getFieldC()));

From your comments to other answers, I don't understand what you want.

Just for the sake of discussion, lets say that the the class did override the equals method.

So your UT will look something like:

SomeType expected = // bla
SomeType actual = // bli

Assert.assertEquals(expected, actual). 

And you are done. Moreover, you can not get the "full equality picture" if the assertion fails.

From what I understand, you are saying that even if the type did override equals, you would not be interested in it, since you want to get the "full equality picture". So there is no point in extending and overriding equals either.

So you have to options: either compare property by property, using reflection or hard-coded checks, I would suggest the latter. Or: compare human readable representations of these objects.

For example, you can create a helper class that serializes the type you wish tocompare to an XML document and than compare the resulting XML! in this case, you can visually see what exactly is equal and what is not.

This approach will give you the opportunity to look at the full picture but it is also relatively cumbersome (and a little error prone at first).

AssertJ assertions can be used to compare the values without #equals method properly overridden, e.g.:

import static org.assertj.core.api.Assertions.assertThat; 

// ...

assertThat(actual)
    .usingRecursiveComparison()
    .isEqualTo(expected);

Can you put the comparision code you posted into some static utility method?

public static String findDifference(Type obj1, Type obj2) {
    String difference = "";
    if (obj1.getFieldA() == null && obj2.getFieldA() != null
            || !obj1.getFieldA().equals(obj2.getFieldA())) {
        difference += "Difference at field A:" + "obj1 - "
                + obj1.getFieldA() + ", obj2 - " + obj2.getFieldA();
    }
    if (obj1.getFieldB() == null && obj2.getFieldB() != null
            || !obj1.getFieldB().equals(obj2.getFieldB())) {
        difference += "Difference at field B:" + "obj1 - "
                + obj1.getFieldB() + ", obj2 - " + obj2.getFieldB();
        // (...)
    }
    return difference;
}

Than you can use this method in JUnit like this:

assertEquals("Objects aren't equal", "", findDifferences(obj1, obj));

which isn't clunky and gives you full information about differences, if they exist (through not exactly in normal form of assertEqual but you get all the info so it should be good).

In common case with AssertJ you can create custom comparator strategy:

assertThat(frodo).usingComparator(raceComparator).isEqualTo(sam)
assertThat(fellowshipOfTheRing).usingElementComparator(raceComparator).contains(sauron);

Using a custom comparison strategy in assertions

AssertJ examples

There is many correct answers here, but I would like to add my version too. This is based on Assertj.

import static org.assertj.core.api.Assertions.assertThat;

public class TestClass {

    public void test() {
        // do the actual test
        assertThat(actualObject)
            .isEqualToComparingFieldByFieldRecursively(expectedObject);
    }
}

UPDATE: In assertj v3.13.2 this method is deprecated as pointed out by Woodz in comment. Current recommendation is

public class TestClass {

    public void test() {
        // do the actual test
        assertThat(actualObject)
            .usingRecursiveComparison()
            .isEqualTo(expectedObject);
    }

}

You can override the equals method of the class like:

@Override
public int hashCode() {
    int hash = 0;
    hash += (app != null ? app.hashCode() : 0);
    return hash;
}

@Override
public boolean equals(Object object) {
    HubRule other = (HubRule) object;

    if (this.app.equals(other.app)) {
        boolean operatorHubList = false;

        if (other.operator != null ? this.operator != null ? this.operator
                .equals(other.operator) : false : true) {
            operatorHubList = true;
        }

        if (operatorHubList) {
            return true;
        } else {
            return false;
        }
    } else {
        return false;
    }
}

Well, if you want to compare two object from a class you must implement in some way the equals and the hash code method

This won't help the OP, but it might help any C# developers who end up here...

Like Enrique posted, you should override the equals method.

Is there a better practice to get what I want from the object, without subclassing and overridding equals (ugh)?

My suggestion is to not use a subclass. Use a partial class.

Partial Class Definitions (MSDN)

So your class would look like...

public partial class TheClass
{
    public override bool Equals(Object obj)
    {
        // your implementation here
    }
}

For Java, I would agree with the suggestion to use reflection. Just remember that you should avoid using reflection whenever possible. It is slow, hard to debug, and even harder to maintain into the future because IDEs could break your code by doing a field rename or something like that. Be careful!

If you're using hamcrest for your asserts (assertThat) and don't want to pull in additional test libs, then you can use SamePropertyValuesAs.samePropertyValuesAs to assert items that don't have an overridden equals method.

The upside is that you don't have to pull in yet another test framework and it'll give a useful error when the assert fails (expected: field=<value> but was field=<something else>) instead of expected: true but was false if you use something like EqualsBuilder.reflectionEquals().

The downside is that it is a shallow compare and there's no option for excluding fields (like there is in EqualsBuilder), so you'll have to work around nested objects (e.g. remove them and compare them independently).

Best Case:

import static org.hamcrest.beans.SamePropertyValuesAs.samePropertyValuesAs;
...
assertThat(actual, is(samePropertyValuesAs(expected)));

Ugly Case:

import static org.hamcrest.beans.SamePropertyValuesAs.samePropertyValuesAs;
...
SomeClass expected = buildExpected(); 
SomeClass actual = sut.doSomething();

assertThat(actual.getSubObject(), is(samePropertyValuesAs(expected.getSubObject())));    
expected.setSubObject(null);
actual.setSubObject(null);

assertThat(actual, is(samePropertyValuesAs(expected)));

So, pick your poison. Additional framework (e.g. Unitils), unhelpful error (e.g. EqualsBuilder), or shallow compare (hamcrest).

Using Shazamcrest, you can do:

assertThat(obj1, sameBeanAs(obj2));

You can use Apache commons lang ReflectionToStringBuilder

You can either specify the attributes you want to test one by one, or better, exclude those you don't want:

String s = new ReflectionToStringBuilder(o, ToStringStyle.SHORT_PREFIX_STYLE)
                .setExcludeFieldNames(new String[] { "foo", "bar" }).toString()

You then compare the two strings as normal. For the point about reflection being slow, I assume this is only for testing, so shouldn't be so important.

As an alternative for junit-only, you can set fields to null prior to equals assertion:

    actual.setCreatedDate(null); // excludes date assertion
    expected.setCreatedDate(null);

    assertEquals(expected, actual);

Mockito offers a reflection-matcher:

For latest version of Mockito use:

Assert.assertTrue(new ReflectionEquals(expected, excludeFields).matches(actual));

For older versions use:

Assert.assertThat(actual, new ReflectionEquals(expected, excludeFields));