how can I reduce my list of structures based on the other list of Strings in Java?

Question

In my Java application I have a class:

public class MyStructure {

    SomeClass someClass;
    String[] fields;

    ...
}

Now, I have a list of the structures above:

List< MyStructure> structures = getStructures();

I also have a list of Strings:

List<String> myList = getStrings();

I need to filter the first list (structures) so that it only contains elements, that in their fields array contain any of the Strings present on myList.

I thought about writing a for loops, something like:

List<MyStructure> outcomeStructures = new ArrayList<>(); 

for (MyStructure mystructure : structures) {
    for (String temp : mystructure.getFields()) {
        if (myList.contains(temp) {
            outcomeStructures.add(mystructure);
        }
    }
}

but maybe there's a better way to do so? Thanks!

have a look into the Java streaming capabilities. I believe this is exactly what you want. — Jochen, Feb 17 '20 at 21:58

score 3 · Accepted Answer · edited Feb 18 '20 at 05:06

3

For the better performance you can convert the List<String> myList = getStrings(); to Set<String> mySet since HashSet time complexity for contains is O(1) always. Then use:

List<MyStructure> outcomeStructures = structures.stream()
        .filter(st -> Arrays.stream(st.getFields()).anyMatch(mySet::contains))
        .collect(Collectors.toList());

edited Feb 18 '20 at 05:06

Naman

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answered Feb 17 '20 at 21:59

Ryuzaki L

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I think there's some problem, the collect function is not visible here, perhaps I should call it on something else than the result of anyMatch, that returns boolean? – randomuser1 Feb 17 '20 at 22:47
@randomuser1 Did you make sure the brackets put in the code are appropriately matched? Try out the current code, I can confirm it compiles successfully. – Naman Feb 18 '20 at 05:09

how can I reduce my list of structures based on the other list of Strings in Java?

1 Answers1