Java 自定义聚合器实现斐波那契数列.md

import java.util.*;
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;
import java.util.stream.Stream;

/**
 * 自定义聚合器，实现一个含 N 个数的斐波那契序列
 */
public class FiboCollector implements Collector<Integer, List<Integer>, List<Integer>> {
    @Override
    public Supplier<List<Integer>> supplier() {
        return () -> {
            List<Integer> result = new ArrayList<>();
            result.add(0);
            result.add(1);
            return result;
        };
    }

    @Override
    public BiConsumer<List<Integer>, Integer> accumulator() {
        return (res, num) -> {
            Integer next = res.get(res.size() - 1) + res.get(res.size() - 2);
            res.add(next);
        };
    }

    @Override
    public BinaryOperator<List<Integer>> combiner() {
        // return (left，right) -> { left.addAll(right); return left; };
        return null;
    }

    @Override
    public Function<List<Integer>, List<Integer>> finisher() {
        return res -> {
            res.remove(0);
            res.remove(1);
            return res;
        };
    }

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

    public static void main(String[] args) {
        // List<Integer> fibo = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).stream().collect(new FiboCollector());
        List<Integer> fibo = Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).collect(new FiboCollector());
        System.out.println(fibo);
    }
}

参考http://www.importnew.com/27901.html