从两个具有相同键和值的列表创建对象

Question

I have 2 lists which contain Objects. These 2 lists can have same Objects in different order.

I have overridden the equals method in the Object such that if one particular property of the object is same as other Object then they are equal even if other properties are not same.

Now I need to create a map where the key is the Object from one list and value is the same Object from the other list. If there is an Object in one list which does not have an equal object in the other list, those Objects should be ignored while creating the Map.

How can i accomplish this using java stream?

Answer 1

I can see why you want to do something like this, but it seems very hacky. I'm sure if you tell us what you're trying to achieve, we can provide you with a better design. Regardless, the following will work with Java 10:

var list1 = List.of("One", "Two", "Three");
var list2 = List.of("Two", "Three", "Four");

var set = Set.copyOf(list2);

var map = list1.stream()
               .filter(set::contains)
               .collect(Collectors.toMap(k -> k, v -> list2.get(list2.indexOf(v))));

System.out.println(map);

Output:

{Two=Two, Three=Three}

The equivalent code written for Java 8 is as follows:

List<String> list1 = Arrays.asList("One", "Two", "Three");
List<String> list2 = Arrays.asList("Two", "Three", "Four");

Set<String> set = new HashSet<>(list2);

// Defined the Map here for formatting reasons.
Map<String, String> map;

map = list1.stream()
           .filter(set::contains)
           .collect(Collectors.toMap(k -> k, v -> list2.get(list2.indexOf(v))));

System.out.println(map);

Note : This assumes that you have overridden Object#hashCode as well as Object#equals .