Htykuut

I'am currently working in a java project which I have a list of strings and I want them to have a specific format using streams .

For example

Input : [nom, contains, b, and, prenom, contains, y, and, age, >=, 1, and, age, <=, 100]
Ouput:

[

{key:"nom",

operation:"contains",

value:"b"

},

{

key:"prenom",

operation:"contains",

value:"y"

},

{

key:"age",

operation:">=",

value: 1

},

{

key:"age",

operation:"<=",

value: 1000

}]

I wrote a very basic code without using streams:

List filter = [nom, contains, b, and, prenom, contains, y, and, age, >=, 1, and, age, <=, 100]

    List<SearchCriteria> formedFilter = new ArrayList<>();

    SearchCriteria sc = new SearchCriteria();

    if(filter != null){

        for(int i = 0 ;i< filter.size();i++){

            if(i % 4 ==0){

                sc.setKey((String) filter.get(i));

            }else if(i % 4 == 1){

                sc.setOperation((String) filter.get(i));



            }else if(i % 4 ==2){

                sc.setValue(filter.get(i));

                formedFilter.add(sc);



            }else{

                sc = new SearchCriteria();

            }

        }

    }

SearchCriteria Class

public class SearchCriteria {

    private String key;

    private String operation;

    private Object value;



    public SearchCriteria() {

    }



    public SearchCriteria(String key, String operation, Object value) {

        this.key = key;

        this.operation = operation;

        this.value = value;

    }



   // getters and setters

}

For a Java 8 version of Aomine's answer you can use:

List<SearchCriteria> formedFilter = IntStream.iterate(0, i -> i + 4)

            .limit(filter.size() / 4 + 1) // + 1 to consider the last group as well

            .mapToObj(i -> new SearchCriteria(filter.get(i), filter.get(i + 1), filter.get(i + 2)))

            .collect(Collectors.toList());

Alternatively, similar to a suggestion by Holger, you can use the rangeClosed API from IntStream as:

List<SearchCriteria> formedFilter2 = IntStream.rangeClosed(0, filter.size() / 4)

        .map(i -> i * 4)

        .mapToObj(i -> new SearchCriteria(filter.get(i), filter.get(i + 1), filter.get(i + 2)))

        .collect(Collectors.toList());

Using JDK 9, you can do:

IntStream.iterate(0, i -> i < source.size(), i -> i + 4)

         .mapToObj(x -> new SearchCriteria(source.get(x), source.get(x + 1), source.get(x + 2)))

         .collect(toList());