Easy way to filter elements from a collection in Java?

Question

I want to write a method that removes all elements from a collection that follow a certain pattern. In functional languages, I would use filter() with a lambda expression. However, in Java, it seems I'm stuck with this:

public void removeAllBlueCars() {     LinkedList<Car> carsToRemove = new LinkedList<Car>();     for (Car c : cars) {         if (c.getCarColor() == Color.BLUE) {             carsToRemove.add(c);         }     }     cars.removeAll(carsToRemove ); } 

Removing elements directly causes a ConcurrentModificationException. Is there a better way to do this without resorting to Google Collections?

Answer 1

With Java 8, you can filter with a lambda expression using Collection.removeIf.

cars.removeIf(c -> c.getCarColor() == Color.BLUE); 

Answer 2

Maybe you could use iterators, which are a little more efficient:

public void removeAllBlueCars() {     Iterator<Car> carsIterator = cars.iterator();     while (carsIterator.hasNext()) {         Car c = carsIterator.next();         if (c.getCarColor() == Color.BLUE) {             carsIterator.remove();         }     } } 

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Also, if you want to make this solution more generic, I'd suggest you something like:

public interface Filter<T> {      public boolean shouldRemove(T t);  } 

And you could use it like this:

public void removeCars(Filter<Car> filter) {     Iterator<Car> carsIterator = cars.iterator();     while (carsIterator.hasNext()) {         Car c = carsIterator.next();         if (filter.shouldRemove(c)) {             carsIterator.remove();         }     } } 

Your method gets called like this:

removeCars(new Filter<Car>() {      public boolean shouldRemove(Car car) {         return car.getCarColor() == Color.BLUE;     }  });