Question

I am trying to use predicates, but I can’t because method overloading is acting up…

I want to use filter with an array (varargs), and I want to use the built-in method in predicates, that filters the array as converted to a list.

This is the error: The method filter(Iterable, Predicate) in the type Predicates is not applicable for the arguments (Class[], Predicate)

private static final Predicate<Method> isTestMethod = new Predicate<Method>() {
    @Override
    public boolean evaluate(Method input) {
        return input.isAnnotationPresent(Test.class);
    }
};

public static void testClasses(Class<?>... classes) {
    for (Method method : filter(classes, isTestMethod)) {

    }
}

This is the predicates methods:

/**
 * Returns the elements of <tt>unfiltered</tt> that satisfy a predicate.
 * 
 * @param unfiltered An iterable containing objects of any type
 * that will be filtered and used as the result.
 * @param predicate The predicate to use for evaluation.
 * @return An iterable containing all objects which passed the predicate's evaluation.
 */
public static <T> Iterable<T> filter(Iterable<T> unfiltered, Predicate<T> predicate) {
    checkNotNull(unfiltered);
    checkNotNull(predicate);

    List<T> result = new ArrayList<T>();
    Iterator<T> iterator = unfiltered.iterator();
    while (iterator.hasNext()) {
        T next = iterator.next();
        if (predicate.evaluate(next)) {
            result.add(next);
        }
    }
    return result;
}

/**
 * Returns the elements of <tt>unfiltered</tt> that satisfy a predicate.
 * 
 * @param unfiltered An array containing objects of any type
 * that will be filtered and used as the result.
 * @param predicate The predicate to use for evaluation.
 * @return An iterable containing all objects which passed the predicate's evaluation.
 */
public static <T> Iterable<T> filter(T[] unfiltered, Predicate<T> predicate) {
    return filter(Arrays.asList(unfiltered), predicate);
}

Answer 1

Your filter is applicable to methods – but you have a collection of classes. You can’t apply your isTestMethod predicate to a class…

What did you anticipate it would do? Were you perhaps looking for a filter to match classes which had any test methods?