CODEWITHSUNDEEP
java-8lambda
Aravind Yarram
Aravind Yarram

Reputation: 80176

Unable to figure out the usage

Following is one of the exercises from Java SE 8 for the Really Impatient.

Form a subclass Collection2 from Collection and add a default method void forEachIf(Consumer action, Predicate filter) that applies action to each element for which filter returns true. How could you use it?

Following is my definition of Collection2. I am unable to figure out how to use it.

public interface Collection2<E> extends Collection<E>
{

    default void forEachIf(Consumer<E> action, Predicate<E> filter)
    {
        forEach(e -> {
            if (filter.test(e))
            {
                action.accept(e);
            }
        });
    }
}

So, I have the following list that i would like to apply the String.toUpperCase action for the strings that start with "a". How would I use Collection2 to achieve that?

public static void ex09()
{
        Collection<String> l = new ArrayList<>();
        l.add("abc");
        l.add("zxx");
        l.add("axc");

        // What next???

}

Upvotes: 4

Views: 127

Answers (1)

dkatzel
dkatzel

Reputation: 31648

You need to make a new class that implements Collection2,

public class ArrayList2<E> extends ArrayList<E> implements Collection2<E>{

}

then just use your new class:

public static void ex09()
{
    Collection2<String> l = new ArrayList2<>();
    l.add("abc");
    l.add("zxx");
    l.add("axc");

    l.forEachIf(  (s)->System.out.println(s.toUpperCase()),
                  (s)-> s.startsWith("a"));


}

Which when run will print:

ABC
AXC

Upvotes: 6

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