Checking the equality of lists of Comparable objects in Groovy - groovy

Question

I'm writing a test using the Spock framework and I found a strange bavior when testing equality of lists.
When I compare two lists like
sourceList == targetList
and those lists contains Comparable objects of the same type, those objects are tested for equality using its compareTo methods instead of equals.
Is there any simple way how to force Groovy to use equals when testing equality on such lists?
Here is a simple test specification where the test should fail, but it does not.
class Test extends Specification {
def "list test"() {
when:
def listA = [[index: 1, text: "1"] as Bean, [index: 2, text: "2"] as Bean]
def listB = [[index: 1, text: "1"] as Bean, [index: 2, text: "3"] as Bean]
then:
listA == listB
}
class Bean implements Comparable<Bean> {
int index
String text
#Override
public int compareTo(Bean o) {
return index.compareTo(o.index);
}
#Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + index;
result = prime * result + ((text == null) ? 0 : text.hashCode());
return result;
}
#Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (!(obj instanceof Bean)) {
return false;
}
Bean other = (Bean) obj;
if (index != other.index) {
return false;
}
if (text == null) {
if (other.text != null) {
return false;
}
} else if (!text.equals(other.text)) {
return false;
}
return true;
}
}
}

Answer 1

Asking for a simple method is subjective. The key to this answer is that, in Groovy, the is() method will check object equality.
Consider this new method on ArrayList. If appropriate, it will zip together the two lists and call is() on each pair of items.
ArrayList.metaClass.myCompare = { listB ->
def result = false
def listA = delegate
if (listB && listA.size() == listB.size()) {
def zipped = [listA, listB].transpose()
result = zipped.inject(true){ ok, pair ->
ok && pair[0].is(pair[1])
}
}
result
}
then:
def beanA = new Bean(index: 1, text: 'a')
def beanA1 = new Bean(index: 1, text: 'a')
def beanB = new Bean(index: 2, text: 'b')
assert [beanA, beanB].myCompare([beanA, beanB])
assert ! [beanA, beanB].myCompare([beanA1, beanB])
assert ! [beanA, beanB].myCompare([beanA])
assert ! [beanA, beanB].myCompare(null)
assert ! [beanA, beanB].myCompare([])

Answer 2

In groovy, "==" is replaced with equals if items are not comparable, or with compareTo if they implement Comparable. I do not know a simple way to force equals, if the collections have no duplicates, you can check the elements of the collection one by one:
def collectionsEqual (Collection<?> collection1, Collection<?> collection2) {
if (collection1.size() != collection2.size()) {
return false
}
for (elem1 in collection1) {
def founded = false;
for (elem2 in collection2) {
if (elem1?.equals (elem2)) {
founded = true
}
}
if (!founded) {
return false
}
}
true
}
but, in https://www.baeldung.com/java-compareto we have:
It is also strongly recommended, though not required, to keep the
compareTo implementation consistent with the equals method
implementation:
x.compareTo(y) == 0 should have the same boolean value as x.equals(y)
This will ensure that we can safely use objects in sorted sets and
sorted maps.