如何使用Lambda表达式填充HashMap

Question

还有一类(SomeOrders),它具有像几个字段Id,Summary,Amount,等...

要求是从对象输入中收集Id作为关键字和Summary值的值.HashMapListSomeOrder

java 8之前的代码:

List<SomeOrder> orders = getOrders();
Map<String, String> map = new HashMap<>();
for (SomeOrder order : orders) {
    map.put(order.getId(), order.getSummary());
}

如何在Java 8中实现与Lambda表达式相同的功能？

Answer 1

用途Collectors.toMap:

orders.stream().collect(Collectors.toMap(SomeOrder::getID, SomeOrder::getSummary));

要么

orders.stream().collect(Collectors.toMap(o -> o.getID(), o -> o.getSummary()));