hashmap - Java 8: Create tuples from Java List -

i looking use java 8s new features create key value pairs java list , insert map

consider list [1, 2, 3, 4]

i looking 2 tuples, [1, 2] , [3, 4]

this code, idea of copied answer similar question

where going wrong? nothing added map.

intstream.range(1, list.size())         .filter(i -> + 1 % 2 == 0)         .maptoobj(i -> new abstractmap.simpleentry<>(list.get(i - 1), list.get(i)))         .foreach(entry -> map.put(entry.getkey(), entry.getvalue())); 

you have entered common java 8 pitfall: have created stream, described how want process it, didn't triggered processed.

after maptoobj call should trigger processing via calling method collect, lets list, , make foreach call. or directly use collectors.toconcurrentmap:

intstream.range(1, list.size())             .filter(i -> (i + 1) % 2 == 0)             .maptoobj(i -> new abstractmap.simpleentry<>(list.get(i - 1), list.get(i)))             .collect(collectors.toconcurrentmap(o -> o.getkey(), o -> o.getvalue()))