Casting – Java 8 – filtering collections with external parameters

I have an animal map containing specific successors

MyBaSEObjectAnimalMap.values().stream().
     filter(x -> x instanceof Dog).
     map(x -> (Dog) x).
     toArray(Dog[]::new);

Is there any way to abstract this?

I want to implement a private method with the following signature:

filterMapByType(Map<String,Animal> map,Class<T extends Animal> type)

Or something like that

Solution

You can provide an intfunction to call toArray, so you can get an array of type t instead of an array of objects

public static <T extends Animal> T[] filterMapByType(Map<String,Class<T> type,IntFunction<T[]> generator) {
    return map.values()
              .stream()
              .filter(type::isinstance)
              .map(type::cast)
              .toArray(generator);
}

Give an example of a telephone call:

Dog[] dogs = filterMapByType(map,Dog.class,Dog[]::new);

Dog []: new is equivalent to length – > new dog [length], that is, a function that takes an int as a parameter and returns an array of type dog with the size of length

If you can return to a list, you can use collect(toList()); instead of. ToArray (generator);