CODEWITHSUNDEEP
javagenericsjunitjava-8java-stream
Ronnie
Ronnie

Reputation: 31

I am struggling with Generics in Java Stream

I know how to utilize intermediate and terminal function with streams, and many other basic things. but the task I have been given is confusing for me to implement. I have been struggling for last 36 hours non-stop. my assignment is as follow:

Implement one static method in a functional way, that takes a List<T>, filters it, orders it, returns only a certain amount of values and skips a certain amount of values and applies a mapping function to it. The returnvalue shall be a List<R>. T and R are unspecified generic types. All needed values shall be parameters. The limit and offset shall be optional. Test your method using JUnit.

so far I could only manage to write the code and I am stuck with first step filter. confusion is, if I don't know type of list how can I filter it.

public class GeneralMethods<T,R> {

    private List<T> recList;
    private List<R> retList;

    public void manipulateList(){
        retList = recList.stream().filter(s -> s.)
    }
}

This is my assignment I have struggled alot, I would appreciate your help.

Upvotes: 3

Views: 298

Answers (1)

Serg M Ten
Serg M Ten

Reputation: 5606

Your one liner should look something like

public class GeneralMethods<T,R> {

    public List<R> manipulateList(List<T> recList,
                                   Predicate<T> filterPredicate,
                                   Comparator<T> comparatorT,
                                   Function<T,R> mapTtoR,
                                   long ... limitAndOffset){

        return recList.stream()
                      .filter(filterPredicate)
                      .sorted(comparatorT)
                      .skip(limitAndOffset.length > 1 ? limitAndOffset[1] : 0)
                      .limit(limitAndOffset.length > 0 ? limitAndOffset[0] : Long.MAX_VALUE)
                      .map(mapTtoR)
                      .collect(toList());
    }

}

Then on the JUnit you must provide implementations of filterPredicate, comparatorT, and mapTtoR parameters.

Upvotes: 2

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