Use of flat map with list of list

Question

If I have a List<List<Foo>> I can use flat map to flatten the list. But I have by MyClass which has a List<Foo> and the Foo class has list of bars List<Bar> then I have to do something like this :

myClass.getFoos().stream().map(Foo::getBars).forEach({
    bar -> // some code
});

Is it possible to use flat map in this scenario so I can get list of bars from MyClass in one shot.

Eugene · Accepted Answer · 2018-10-10 08:52:12Z

3

Try this:

myClass.getFoos().stream()
    .map(Foo::getBars)
    .flatMap(List::stream) // flatten the lists
    .forEach(...);

Note the exlcusive use of method references, which I find neater and easier to read than lambdas.

edited Oct 10, 2018 at 8:52

Eugene

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answered Oct 10, 2018 at 0:02

Bohemian♦

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1 Comment

fastcodejava Over a year ago

Great, I didn't know I can do flat map after map.

Eugene · Accepted Answer · 2018-10-09 20:56:36Z

3

myClass.getFoos()
        .stream() 
        .flatMap(x -> x.getBars().stream())
        .forEach(...)

answered Oct 9, 2018 at 20:56

Eugene

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