62. Tackling type patterns for instanceof and streams

Let’s consider a List<Engine> where Engine is an interface implemented by several classes such as HypersonicEngine, HighSpeedEngine, and RegularEngine. Our goal is to filter this List and eliminate all RegularEngine classes that are electric and cannot pass our autonomy test. So, we can write code as follows:

public static List<Engine> filterRegularEngines(
              List<Engine> engines, int testSpeed) {
  for (Iterator<Engine> i = engines.iterator(); i.hasNext();){
    final Engine e = i.next();
    if (e instanceof RegularEngine) {
      final RegularEngine popularEngine = (RegularEngine) e;
      if (popularEngine.isElectric()) {
        if (!hasEnoughAutonomy(popularEngine, testSpeed)) {
          i.remove();
        }
      }
    }
  }
  return engines;
}

But, starting with JDK 8, we can safely remove from a List without using an Iterator via a default method from java.util.Collection named public default boolean removeIf(Predicate<? super E> filter). If we combine this method (and, therefore, the Stream API) with type patterns for instanceof, then we can simplify the previous code as follows:

public static List<Engine> filterRegularEngines(
              List<Engine> engines, int testSpeed) {
  engines.removeIf(e -> e instanceof RegularEngine engine 
    && engine.isElectric()
    && !hasEnoughAutonomy(engine, testSpeed));
  return engines;
}

So, whenever you have the chance to use type patterns with the Stream API, don’t hesitate.