我有一个对象列表。首先,我需要按类型对其进行排序。
比按面值。最后,总结所有数量:
class Coin{
String type;
BigInteger faceValue;
BigInteger quantity;
...
}
List<Coin> coins = new ArrayList<>();
coins.add(new Coin("USD", 1, 150));
coins.add(new Coin("USD", 1, 6));
coins.add(new Coin("USD", 1, 60));
coins.add(new Coin("USD", 2, 100));
coins.add(new Coin("USD", 2, 100));
coins.add(new Coin("CAD", 1, 111));
coins.add(new Coin("CAD", 1, 222));
结果列表必须仅包含 3 个新硬币对象:
Coin("USD", 1 , 216)
Coin("USD", 2 , 200)
Coin("CAD", 1 , 333)
这怎么能只用一个 lambda 表达式来写呢?