[四] java8 函数式编程 收集器浅析 收集器Collec…

/**
* Simple implementation class for {@code Collector}.
*
* @param <T> the type of elements to be collected
* @param <R> the type of the result
*/
static class CollectorImpl<T, A, R> implements Collector<T, A, R> {
private final Supplier<A> supplier;
private final BiConsumer<A, T> accumulator;
private final BinaryOperator<A> combiner;
private final Function<A, R> finisher;
private final Set<Characteristics> characteristics;

CollectorImpl(Supplier<A> supplier,
BiConsumer<A, T> accumulator,
BinaryOperator<A> combiner,
Function<A,R> finisher,
Set<Characteristics> characteristics) {
this.supplier = supplier;
this.accumulator = accumulator;
this.combiner = combiner;
this.finisher = finisher;
this.characteristics = characteristics;
}

CollectorImpl(Supplier<A> supplier,
BiConsumer<A, T> accumulator,
BinaryOperator<A> combiner,
Set<Characteristics> characteristics) {
this(supplier, accumulator, combiner, castingIdentity(), characteristics);
}

@Override
public BiConsumer<A, T> accumulator() {
return accumulator;
}

@Override
public Supplier<A> supplier() {
return supplier;
}
@Override
public BinaryOperator<A> combiner() {
return combiner;
}
@Override
public Function<A, R> finisher() {
return finisher;
}
@Override
public Set<Characteristics> characteristics() {
return characteristics;
}
}

Collector<T, ?, List<T>> toList() {
return new CollectorImpl<>( (Supplier<List<T>>) ArrayList::new,
List::add,
(left, right) -> { left.addAll(right); return left; },
CH_ID);
}