Java - Filter repeats in an array of strings keeping the order

The problem is the use of HashSet , the option is the use of LinkedHashSet , since LinkedHashSet stores the elements according to the order of insertion:

   String[] strs = {"orange", "apple", "apple", "banana", "grape", "apple", "lemon"};

     List<String> arr = Arrays.asList(strs);
    Set<String> hs   = new LinkedHashSet ();
    hs.addAll(arr);

As a result you would get:

   {orange, apple, banana, grape, lemon}

Something important to comment is that using HashSet has better performance but does not guarantee any order in the elements, instead LinkedHashSet yes, but performance is sacrificed.

By using Stream it becomes simple.

public class FiltrarRepeticiones {
    public static void main(String[] args) {
        String[] strs = {"orange", "apple", "apple", "banana", "grape", "apple", "lemon"};
        List<String> list = Arrays.asList(strs);
        Stream<String> listaNueva = list.stream().distinct();
        listaNueva.forEach(fruta -> System.out.println(fruta));   
    } 
}

  

Result:   orange apple banana grape lemon

Update. This way you could work with the functional interfaces . I'll give an example with the interface UnaryOperator , which receives a type and returns a value of the same type.

public interface UnaryOperator<T> extends Function<T,T>

Ex:

public class UnaryOperatorTest {
    public static void main(String[] args) {
        List<String> listaStr = 
                Arrays.asList("orange", "apple", "apple", "banana", "grape", "apple", "lemon");

        List<String> listStrAct = operadorUnaryStr(cadena -> cadena.toUpperCase(), listaStr);
        listStrAct.stream().distinct().forEach(str -> System.out.print(str+" "));

    }

    public static List<String> operadorUnaryStr(
                UnaryOperator<String> unaryOpt, List<String> lista){
        List<String> listaActualizada = new ArrayList<>();
        lista.forEach(str -> listaActualizada.add(unaryOpt.apply(str)));
        return listaActualizada;  
    }

}

  

And we would get as a result ...   ORANGE APPLE BANANA GRAPE LEMON

With Streams you can remove repeated values and have an array again without creating other collections. In addition, the Arrays library makes the work of manipulating arrays much easier.

String[] strs = {"orange", "apple", "apple", "banana", "grape","apple","lemon"};
String[] str = Arrays.stream(strs)
            .distinct()
            .toArray(String[]::new);

System.out.println(Arrays.toString(str));