Java 8 Streams - Apply fixed amount of predicate filters to single Stream

Question

Is there a way to apply fixed amount of Predicates to an opened Stream ? I really can't get any attempt of mine to work. Either the attempt ends up with stream closed error or not all filters are applied.

Example:

 // list of all JLabels of any container
private final List<JLabel> listOfLabels = new ArrayList<>();
// set of user-defined filters
private final Set<Predicate<JLabel>> filters = new HashSet<>();

// let's add some filters
filters.add(label -> label.getBackground() == Color.RED);
filters.add(label -> label.getWidth() > 500);

How can I apply all filter to the Stream of listOfFiles ? Let's say we want to hide JLabels NOT matching these filters. I am looking for something like a non-working code snippet below.

public void applyFilters() {
   listOfLabels.forEach(label -> label.setVisible(false)); // hide all labels
   Stream<JLabel> stream = listOfLabels.stream();
   filters.forEach(stream::filter);
   stream.forEach(label -> label.setVisible(true));
   // stream closed error
}

After method applyFilters() is executed, the container should have visible only labels matching all predicates defined by filters set. (red background and width greater than 500 in this example).

Answer 1

When you work with Stream you have to always use the link to Stream object that was return by applying previous operation. As you can see from the API:

Stream<T> filter(Predicate<? super T> predicate);

The Stream object is returned and javadoc says:

Returns a stream consisting of the elements of this stream that match * the given predicate.

Having this in mind, in your case, we can apply something like the following:

Convert:

filters.forEach(stream::filter);

To:

   for (Predicate<JLabel> filter : filters) {
        stream = stream.filter(filter);
   }

That should work, since now you update the link to the Stream object and follow documentation.