Java新特性解读JDK8之流操作reduce函数

Optional<T> reduce(BinaryOperator<T> accumulator);
T reduce(T identity, BinaryOperator<T> accumulator);


//accumulator参数是函数式接口              
@FunctionalInterface
public interface BinaryOperator<T> extends BiFunction<T,T,T>{
}

package com.example.streamdemo;


import java.util.Arrays;
import java.util.List;
import java.util.Optional;


public class ReduceDemo {
  public static void main(String[] args) {
    //累加计算
    List<Integer> list = Arrays.asList(1,2,3,4);
    Optional<Integer> optional = list.stream().reduce((a,b)->a+b);
    System.out.println(optional.get());
    //求集合中最大值
    Optional<Integer> optional2 = list.stream().reduce((a,b)->a>b?a:b);
    System.out.println(optional2.get());
    //初始值累加计算
    Integer integer = list.stream().reduce(20, (a,b)->a+b);
    System.out.println(integer);
  }
}