[四] java8 函数式编程 收集器浅析 收集器Collector常用方法 运行原理 内部实现详解编程语言

/** 
* 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); 
}