List<Integer> list = new ArrayList<>();
list.add(3);
list.add(7);
list.add(2);
IntSummaryStatistics collect = list.stream().collect(Collectors.summarizingInt(value -> value));
System.out.println(collect);
System.out.println("统计集合元素的个数：" + collect.getCount());
System.out.println("集合元素累加之和：" + collect.getSum());
System.out.println("集合中最小值：" + collect.getMax());
System.out.println("集合中最大值：" + collect.getMin());
System.out.println("集合中平均值：" + collect.getAverage());

打印结果：
IntSummaryStatistics{count=3, sum=12, min=2, average=4.000000, max=7}
统计集合元素的个数：3
集合元素累加之和：12
集合中最小值：7
集合中最大值：2
集合中平均值：4.0

Person p1 = new Person("张三", new BigDecimal("10.0"));
Person p2 = new Person("王五", new BigDecimal("10.0"));
Person p3 = new Person("李四", new BigDecimal("10.0"));
Person p4 = new Person("王五", new BigDecimal("10.0"));
Person p5 = new Person("赵六", new BigDecimal("10.0"));
List<Person> pList = new ArrayList<>();
pList.add(p1);
pList.add(p2);
pList.add(p3);
pList.add(p4);
pList.add(p5);

BigDecimal reduce = pList.stream().map(Person::getSalary).reduce(BigDecimal.ZERO, BigDecimal::add);
System.out.println("工资总计：" + reduce);

打印结果：
工资总计：50.0