How can I turn a List of Lists into a List in Java 8?
If I have a List, how can I turn that into a List that contains all the objects in the same iteration order
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The
flatMapmethod onStreamcan certainly flatten those lists for you, but it must createStreamobjects for element, then aStreamfor the result.You don't need all those
Streamobjects. Here is the simple, concise code to perform the task.// listOfLists is a ListBecause a
ListisIterable, this code calls the forEach method (Java 8 feature), which is inherited fromIterable.Performs the given action for each element of the
Iterableuntil all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified.And a
List'sIteratorreturns items in sequential order.For the
Consumer, this code passes in a method reference (Java 8 feature) to the pre-Java 8 method List.addAll to add the inner list elements sequentially.Appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's iterator (optional operation).
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