Is there an equivalent of Javascript's Array.map in Java?
I have been playing with Java 8 :
List<Long> roleList = siteServiceList.stream()
.map(s -> s.getRoleIdList()).collect(Collectors.toList());
but this doesn't work I don't know why the warning says Incompatible Type.
How can I do this in Java8?
If roleIdList is a List<Long> and you want to get a List<Long> you have to use flatMap instead :
List<Long> roleList = siteServiceList.stream()
.flatMap(s -> s.getRoleIdList().stream())
.collect(Collectors.toList());
If you insist using map the return type should be List<List<Long>> :
List<List<Long>> roleList = siteServiceList.stream()
.map(MyObject::getRoleIdList)
.collect(Collectors.toList());