How to populate a HashMap using a Lambda Expression

Question

There is one class (SomeOrders), which has few fields like Id, Summary, Amount, etc...

The requirement is to collect Id as key and Summary as value to a HashMap from an input List of SomeOrder objects.

Code in Before java 8:

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

How to achieve the same with Lambda expression in Java 8?

Yes, almost same. stackoverflow.com/questions/4138364/… But above is just asked in general, from that one answer can find with Lambda expression. Anyhow thanks for notifying me. — Paramesh Korrakuti
– Paramesh Korrakuti, Commented Mar 23, 2015 at 11:09
Don't get confuse among lambda expression and stream functional operations. I think you would like to get answer for functional operations, as the answer below. — Alex
– Alex, Commented Oct 4, 2017 at 3:11

bvrakvs · Accepted Answer · 2017-10-04 03:05:35Z

37

Use Collectors.toMap :

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

or

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

edited Oct 4, 2017 at 3:05

bvrakvs

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answered Mar 23, 2015 at 10:21

Eran

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2 Comments

prime Over a year ago

What if the orders list has duplicates and the map should have a List to collect the order summaries ? List<> to Map<String, List<String>>

insanely_sin Over a year ago

How to populate an EnumMap like this ?

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