Simple wrapper around Java Collectors to use methods

CollectorIdentityObject.java

import java.util.EnumSet;
import java.util.Set;
import java.util.stream.Collector;

public interface CollectorIdentityObject<T, A, R> extends CollectorObject<T, A, R> {
    @Override
    @SuppressWarnings("unchecked")
    default R finish(A a) {
        return (R) a;
    }

    @Override
    default Set<Characteristics> characteristics() {
        return EnumSet.of(Collector.Characteristics.IDENTITY_FINISH);
    }
}

CollectorObject.java

import java.util.Collections;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;

public interface CollectorObject<T, A, R> extends Collector<T, A, R> {
    A supply();

    void accumulate(A a, T t);

    A combine(A a1, A a2);

    R finish(A a);

    @Override
    default Supplier<A> supplier() {
        return this::supply;
    }

    @Override
    default BiConsumer<A, T> accumulator() {
        return this::accumulate;
    }

    @Override
    default BinaryOperator<A> combiner() {
        return this::combine;
    }

    @Override
    default Function<A, R> finisher() {
        return this::finish;
    }

    @Override
    default Set<Characteristics> characteristics() {
        return Collections.emptySet();
    }
}