Question

I need to write a method that returns a view of a List(java.util.List). The returned view should contain only those elements in the input List that returns true when tested with the isSuccessful() method.

List<Entity> getSuccessfulEntities(List<Entity> entities)
{
  //Return a List view of entities, each element of which returns true for isSuccessful(entity)
}

I have looked at Collections and List API but couldn’t find any facility for this. Any out of box thought?

Answer 1

There’s nothing (at least that I know of) in the Java standard library, but you could use
com.google.common.collect.Collections2.filter() and Predicate, which is just defined as:

public interface Predicate<T> { boolean apply(T input); }

Changes to the unfiltered and filtered Collection affect one another. Sample code:

Predicate<Entity> isSuccessful = new Predicate<Entity>() {
    public boolean apply(Entity e) {
        return e.isSuccessful();
    }
};

Collection<Entity> successfulEntities = filter(entities, isSuccessful);

Related: Java: What is the best way to filter a Collection?