初始数据List AnimalList = (new Animal("dog", 6),
new Animal("dog", 6),
new Animal("cat", 7), new Animal("cat", 7),
new Animal("cat", 7), new Animal("pig",8));
1)计数Map map = ().
collect((Animal::getName,()));
输出结果：{cat=3, dog=2, pig=1}
2) 排序(逆序)().stream().sorted(().reversed())
.forEachOrdered(::println);
3) 累加求和Map sumMap = ().collect.
((Animal::getName, (Animal::getPrice)));
输出结果是：{cat=21, dog=12, pig=8}
4) 分组:Map> groupMap =
().collect((Animal::getName,
(Animal::getPrice, ())));