To be specific, I have two lists:
List<SystemUserWithNameAndId> list1;
List<SystemUserWithNameAndId> list2;
I want to check if they contain the same system users and ordering is not an issue. I tried to use a comparator to sort them first and then check if they're equal using the equals() method of lists. But I don't want to override the equals method for SystemUserWithNameAndId and I was wondering if I could use the comparator I created for sorting or a similar one to check for equality without explicitly iterating through the lists after sorting.
Comparator<SystemUserWithNameAndId> systemUserComparator = new Comparator<SystemUserWithNameAndId>()
{
@Override
public int compare(SystemUserWithNameAndId systemUser1, SystemUserWithNameAndId systemUser2)
{
final int systemUserId1 = systemUser1.getSystemUserId();
final int systemUserId2 = systemUser2.getSystemUserId();
return systemUserId1 == systemUserId2
? 0
: systemUserId1 - systemUserId2;
}
};
Collections.sort(systemUsers1, systemUserComparator);
Collections.sort(systemUsers2, systemUserComparator);
return systemUsers1.equals(systemUsers2);
Ideally, I want to be able to say,
CollectionUtils.isEqualCollections(systemUsers1, systemUsers2, someCustomComparator);
Just implement the method that iterates, and reuse it every time you need it:
public static <T> boolean areEqualIgnoringOrder(List<T> list1, List<T> list2, Comparator<? super T> comparator) {
// if not the same size, lists are not equal
if (list1.size() != list2.size()) {
return false;
}
// create sorted copies to avoid modifying the original lists
List<T> copy1 = new ArrayList<>(list1);
List<T> copy2 = new ArrayList<>(list2);
Collections.sort(copy1, comparator);
Collections.sort(copy2, comparator);
// iterate through the elements and compare them one by one using
// the provided comparator.
Iterator<T> it1 = copy1.iterator();
Iterator<T> it2 = copy2.iterator();
while (it1.hasNext()) {
T t1 = it1.next();
T t2 = it2.next();
if (comparator.compare(t1, t2) != 0) {
// as soon as a difference is found, stop looping
return false;
}
}
return true;
}
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