1 BigDecimal类型数值累加求和

1.1 for循环实现

List<BigDecimal> list=new ArrayList<>();
BigDecimal sum=new BigDecimal(0);
for(BigDecimal decimal:list){
    sum=sum.add(decimal);
}

1.2 stream().reduce()实现

List<BigDecimal> list=new ArrayList<>();
BigDecimal sum=list.stream().reduce(0,BigDecimal::add);

2 Integer类型数值累加求和

2.1 for循环实现

List<Integer> list=new ArrayList<>();
Integer sum=0;
for(Integer i:list){
    sum+=i;
}

2.2 stream().reduce()实现

List<Integer> list=new ArrayList<>();
//lambda表达式实现
Integer sum = list.stream().reduce(0, (current, number) -> current + number);
//方法引用实现
Integer sum2 = list.stream().reduce(0, Integer::sum);

2.3 Collectors.summingInt()实现

List<Integer> list=new ArrayList<>();
long sum = list.stream().collect(Collectors.summingInt(x -> x));

2.4 Collectors.summarizingInt()实现

        List<Integer> list = new ArrayList<>();
        IntSummaryStatistics summaryStatistics = list.stream().collect(Collectors.summarizingInt(x -> x));
        long sum = summaryStatistics.getSum();

3 Long类型数值累加求和

3.1 for循环实现

List<Long> list=new ArrayList<>();
Long sum=0L;
for(Long i:list){
    sum+=i;
}

3.2 stream().reduce()实现

List<Long> list=new ArrayList<>();
//lambda表达式实现
Long sum = list.stream().reduce(0L, (current, number) -> current + number);
//方法引用实现
Long sum2 = list.stream().reduce(0L, Long::sum);

3.3 Collectors.summingLong()实现

List<Long> list=new ArrayList<>();
long sum = list.stream().collect(Collectors.summingLong(x -> x));

3.4 Collectors.summarizingInt()实现

        List<Long> list = new ArrayList<>();
        LongSummaryStatistics summaryStatistics = list.stream().collect(Collectors.summarizingLong(x -> x));
        long sum = summaryStatistics.getSum();

4 Double类型数值累加求和

4.1 for循环实现

List<Double> list = new ArrayList<>();
Double sum = 0d;
for (Double i : list) {
    sum += i;
}

注意 Double小数点失真问题解决 : 先把Double转为BigDecimal，再求和。代码如下 :

		List<Double> list = new ArrayList<>();
        list.add(1.24224D);
        list.add(1.24224D);
        list.add(1.32224D);
        BigDecimal bSum = new BigDecimal(0);
        for (Double i : list) {
            bSum = bSum.add(BigDecimal.valueOf(i));
        }
        System.out.println(bSum.doubleValue());