How to use Collection remove if his list meet a condition?

Question

I have a list with some Person Object. Here is my Person class:

public class Person(){
// contructors 

private String lastname;

private String firstname;

private List<Place> places;

// getters and setters
}

My Place class is :

public class Place(){
// contructors 

private String town;

// getters and setters
}

I have code to remove some places from person:

List<Person> persons = new ArrayList<Person>();
// adding persons to List
// Below i want to remove person whose place is in town Paris.
persons.removeIf((Person person)-> person.getPlaces(???));

I want to remove a person from the list whose Place meets the following condition place.getTown()=="Paris"

How to write this code?

@RC. [`Collection.removeIf`](https://docs.oracle.com/javase/8/docs/api/java/util/Collection.html#removeIf-java.util.function.Predicate-) is a standard method in Java — Mark Rotteveel, Dec 27 '17 at 12:02
@MarkRotteveel I know, my point was if you can write a removeIf you can answer the question — , Dec 27 '17 at 12:26
@RC. That is a rather circular argument, and not helpful at all. — Mark Rotteveel, Dec 27 '17 at 12:37

score 10 · Accepted Answer · answered Dec 27 '17 at 12:16

10

Add a method hasPlace to Person class:

public boolean hasPlace(String townName) {
    return places.stream()
            .map(Place::getTown)
            .anyMatch(townName::equals);
}

Then, you can use this in the predicate given to the removeIf statement:

persons.removeIf(person -> person.hasPlace("Paris"));

answered Dec 27 '17 at 12:16

Ward

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Thank yo for your answer. I tried it but it just removes places from person and not the person which place is Paris. Am i miss something ? – Pracede Dec 27 '17 at 13:56
1

What you say is not possible: this code will only READ places from a person, and shouldn't ouch anything. Maybe you can post your complete code to check? – Ward Dec 27 '17 at 15:51

score 6 · Answer 2 · answered Dec 27 '17 at 11:55

6

Stream over the list of Places to determine if it contains a Place whose town is "Paris":

persons.removeIf(p-> p.getPlaces().stream().anyMatch(pl->pl.getTown().equals("Paris")));

answered Dec 27 '17 at 11:55

Eran

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Why not do: collectionName.removeIf(x -> x.getName().equals(name_to_compare)); ? – whatamidoingwithmylife Dec 27 '17 at 12:35
@GCP Because the `Person` class doesn't contain the name you have to compare to "Paris". You have to check the `getPlaces()` list for instances of `Places` that contain the town "Paris". – Eran Dec 27 '17 at 12:37
I just noticed there is only one field in that class. My bad. – whatamidoingwithmylife Dec 27 '17 at 12:40
Thank yo for your answer. I tried it but it just removes places from person and not the person which place is Paris. Am i miss something ? – Pracede Dec 27 '17 at 14:39
2

@Pracede `persons.removeIf()` can only remove `Person` instance from the `persons` `List`. It does not mutate the elements it removes, so what you describe is not possible. – Eran Dec 27 '17 at 14:42

GuyKhmel · Answer 3 · 2017-12-27T12:41:47.080

0

If you don't want to use removeIf method, you could use Filter to

persons.stream().filter(p-> !p.getPlaces().stream().anyMatch(pl->pl.getTown().equals("Paris")));

edited Dec 27 '17 at 12:41

answered Dec 27 '17 at 11:53

GuyKhmel

505
5
15

1

You need to invert the filter, because now you get all the people which have a place `"paris"` – Lino Dec 27 '17 at 12:16
Fixed. Thanks. :) – GuyKhmel Dec 27 '17 at 12:42

How to use Collection remove if his list meet a condition?

3 Answers3