How to map and filter a list with Java lambda expressions

In this short tutorial, we will see how to map and filter a list with Java lambdas.

Let’s start from a list of integers:

List<Integer> list = List.of(1, 3, 6, 2, 4, 5);

To map the list, we need to convert it into a stream, then map it and finally collect it:

list = list.stream().map(i -> 2 * i).collect(Collectors.toList());

Here each element is multiplied by 2.

To filter a list, we need to convert it into a stream, then filter it and finally collect it:

list = list.stream().filter(i -> i < 10).collect(Collectors.toList());

Here we only keep elements smaller than 10.

If you run the code above, you will get this result in the console:

Original: [1, 3, 6, 2, 4, 5]
Mapped: [2, 6, 12, 4, 8, 10]
Filtered: [2, 6, 4, 8]

which is the expected result.

That’s it for this tutorial ! If you have any question, please leave a reply below, we answer within 24 hours.

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