2c:T486,It is possible to get a `Stream` from any `Collection` by calling `Collection#stream`. Similarly, it is possible to get a `Stream` from an array using `Arrays.stream`: ```java List someList = List.of("Hello", "World"); Stream listStream = someList.stream(); String[] someArray = new String[]{"Hello", "World"}; Stream listStream = Arrays.stream(someArray); ``` Common terminal operations include `toList` which gets a `List` with all elements of the `Stream` or `collect` which allows collecting the elements with a custom `Collector`. ```java List streamConvertedToList = List.of("Hello", "World").stream().toList();//get a list back from the stream Map> groupedByFirstCharacter = List.of("Hello", "World").stream().collect(Collectors.groupingBy(str -> str.charAt(0)));//{H=[Hello], W=[World]} ``` Similarly, it is possible to use `finyAny`/`findFirst` which get a single element from the `Stream` wrapped in an `Optional` or `Optional.empty()` if there are no such elements: ```java List someList = List.of("Hello", "World"); Optional someElement = someList.stream().findAny(); ```2d:T44b,Between the source and the terminal operations, it is possible to add intermediate operations. For example, `filter` can be used to only include elements matching a condition: ```java List streamConvertedToList = List.of("Hello", "World") .stream() .filter(str -> str.startsWith("H"))//ignore elements not starting with H .toList();//List containing Hello ``` Another common intermediate operations is `map` which transforms all object using a function: ```java List lengths = List.of("Hello", "World") .stream() .map(str -> str.length())//convert all Strings to their lengths .toList();//5, 5 ``` Similar to that, the method `flatMap` accepts a function that converts each object to a `Stream` and allows processing all elements of all streams returned by the function. ```java List.of("Hello", "World") .stream() .flatMap(str -> str.chars().boxed())//chars().boxed() returns a Stream containing all chars of the String as Integer objects .toList();//list of all characters/code points in the original Strings: [72, 101, 108, 108, 111, 87, 111, 114, 108, 100] ```

Week 48 — What are `Stream`s (from `java.util.stream`) and how can they process data?

Week 48 — What are `Stream`s (from `java.util.stream`) and how can they process data?

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