Filter Java stream if specific object is a null

Question

I have the object FastFood. In ArrayList there are 10 hotdogs.

public class FastFood {
    ArrayList<Hotdog> hotdogs;
    boolean isTasty;
}

public class Hotdog {
    String name;
    Ingredients ingredients;
}

For 9 hotdogs all data is filled. For 1 hotdog, the object Ingredients is null.

How can I modify below metod to have only these hotdogs, which have filled Ingredients? (I would like to see 9 hotdogs).

public List<Hotdog> convert(Fastfood fastfood) {
      List<Hotdog> hotdogs = fastfood.getHotdogs().stream()
                    .map(this::convertToHotdog)
                    .collect(Collectors.toList());

To remove objects with null property you need to apply filter(), or if you don't need them at all you can use fastfood.getHotdogs().removeIf(hd -> hd.getIngredients() == null); instead of creating a stream. What does the method convertToHotdog is meant to do? getHotdogs() returns a list of Hotdogs and result is also List<Hotdog>, so what is happening in between? — Alexander Ivanchenko
– Alexander Ivanchenko, Commented Jun 10, 2022 at 14:07

Ashish Patil · Accepted Answer · 2022-06-10 14:24:00Z

2

Based on comments & question, it looks like convertToHotdog might be something to do with internal conversion of Hotdog which is not shared as a part of question. In that case, below might be useful:

List<Hotdog> hotdogs = fastfood.getHotdogs().stream()
                    .filter(t->Objects.nonNull(t.getIngredients()))
                    .map(this::convertToHotdog)
                    .collect(Collectors.toList());

answered Jun 10, 2022 at 14:24

Ashish Patil

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1 Comment

M. Justin Over a year ago

Minor, but Objects.nonNull exists mainly to be used as a method lambda; != null would be more idiomatic. .filter(t->t.getIngredients() != null)

Nemanja · Accepted Answer · 2022-06-10 13:49:00Z

2

If you have list of hotdog objects, you can use filter() method, like this:

List<Hotdog> hotdogs = fastfood.getHotdogs().stream()
                    .filter(hotdog->hotdog.getIngredients()!=null)
                    .collect(Collectors.toList());

NOTE: I'm assuming that you have getter method for ingredients field in Hotdog class which is called getIngredients()

edited Jun 10, 2022 at 13:49

answered Jun 10, 2022 at 13:31

Nemanja

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6 Comments

fat_pikachu Over a year ago

is there any way to do it before .map() method?

Nemanja Over a year ago

I don't understand why do you need this method convertToHotdog? You already have list of hotdogs. This fastfood.getHotdogs().stream() will give you stream of hotdog objects.

fat_pikachu Over a year ago

it's received from external service in a crazy way and need advanced mapping :D this is why I'm trying to do this before .map() if this is possible

Nemanja Over a year ago

But this fastfood.getHotdogs() will give you list of hotdogs, rights?

fat_pikachu Over a year ago

yes but I'm getting nullpointer in .map()

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