Java - merge two lists removing duplicates based on the value of a property - collections

Question

I have a class like this:
public class MyObject {
private Long id;
private String firstProp;
private String secondProp;
private Boolean isLatest;
}
In my app, I get two lists, one that will definitely have isLatest set (Boolean.TRUE or Boolean.FALSE) and the other list that will definitely have isLatest set to null
I want a resulting List or Set which contains items from both lists but duplicates removed where isLatest == null. That is, while removing duplicates, I want to retain the elements where isLatest != null. The definition of duplicates is same id.
equals() and hashCode() methods in MyObject are based on id, firstProp and secondProp and cannot be changed as they are predefined and changing them will disturb other parts of the app.
List<MyObject> listWithIsLatestSet = list with items below
myObj1 --> id = 1, isLatest = true;
myObj2 --> id = 2, isLatest = false;
myObj3 --> id = 3, isLatest = true;
myObj4 --> id = 4, isLatest = true;
List<MyObject> listWithIsLatestNull = list with items below
myObj5 --> id = 1, isLatest = null;
myObj6 --> id = 2, isLatest = null;
myObj7 --> id = 5, isLatest = null;
The resulting list would look like below:
myObj1 --> id = 1, isLatest = true;
myObj2 --> id = 2, isLatest = false;
myObj3 --> id = 3, isLatest = true;
myObj4 --> id = 4, isLatest = true;
myObj7 --> id = 5, isLatest = null;
Can this be advised, please?
THIS WORKED FOR ME
import lombok.Builder;
import lombok.EqualsAndHashCode;
import lombok.Getter;
import lombok.ToString;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class MAIN {
public static void main(String[] args) {
Set<MyObject> setWithIsLatestSet = getSetWithIsLatestSet();
Set<MyObject> setWithIsLatestNull = getSetWithIsLatestNull();
setWithIsLatestSet.addAll(setWithIsLatestNull);
setWithIsLatestSet.forEach(System.out::println);
}
private static Set<MyObject> getSetWithIsLatestSet() {
MyObject obj1 = MyObject.builder().id(new Long(1)).isLatest(Boolean.TRUE).build();
MyObject obj2 = MyObject.builder().id(new Long(2)).isLatest(Boolean.FALSE).build();
MyObject obj3 = MyObject.builder().id(new Long(3)).isLatest(Boolean.TRUE).build();
MyObject obj4 = MyObject.builder().id(new Long(4)).isLatest(Boolean.TRUE).build();
MyObject obj5 = MyObject.builder().id(new Long(5)).isLatest(Boolean.TRUE).build();
return Stream.of(obj1, obj2, obj3, obj4, obj5).collect(Collectors.toCollection(HashSet::new));
}
private static Set<MyObject> getSetWithIsLatestNull() {
MyObject obj1 = MyObject.builder().id(new Long(1)).build();
MyObject obj2 = MyObject.builder().id(new Long(2)).build();
MyObject obj6 = MyObject.builder().id(new Long(6)).build();
MyObject obj7 = MyObject.builder().id(new Long(7)).build();
return Stream.of(obj1, obj2, obj6, obj7).collect(Collectors.toCollection(LinkedHashSet::new));
}
}
#EqualsAndHashCode(onlyExplicitlyIncluded = true)
#Getter
#Builder
#ToString
class MyObject {
#EqualsAndHashCode.Include
private Long id;
private Boolean isLatest;
}
Output:
MyObject(id=5, isLatest=true)
MyObject(id=6, isLatest=null)
MyObject(id=7, isLatest=null)
MyObject(id=1, isLatest=true)
MyObject(id=2, isLatest=false)
MyObject(id=3, isLatest=true)
MyObject(id=4, isLatest=true)

Answer 1

You can try this. Work fine for your example,
BinaryOperator<MyObject> mergeFunction = (old, lst) -> {
if (lst.getLatest() != null && lst.getLatest()) {return lst;}
else if (old.getLatest() == null && lst.getLatest() == null) {return lst;}
else if (old.getLatest() == null && lst.getLatest() != null && !lst.getLatest()) {return lst;}
else {return old;}
};
List<MyObject> collect = new ArrayList<>(Stream.concat(listWithIsLatestSet.stream(), listWithIsLatestNull.stream())
.collect(Collectors.toMap(MyObject::getId, Function.identity(), mergeFunction))
.values());