"Here, we collect to a Map, where each key is the String's length and each value is the name itself: Map<Integer, String> map = names.stream() .collect(Collectors.toMap( String::length, n -> n )); If multiple names share the same length, a collision occurs. Handle it with a merge function: Map<Integer, String> safeMap = names.stream() .collect(Collectors.toMap( String::length, n -> n, (a, b) -> a // keep the first value if keys collide ));"
"Collectors.joining() merges all stream elements into one String using any delimiter you choose. You can use " |", ";", or even "\n " to separate values however you like: List<String> names = List.of("Bill", "James", "Patrick"); String result = names.stream() .map(String::toUpperCase) .collect(Collectors.joining(", ")); System.out.println(result); The output here will be: BILL, JAMES, PATRICK."
"Collectors.groupingBy() groups elements by key (here it's string length) and returns a Map<Key, List<Value>>: List<String> names = List.of("james", "linus", "john", "bill", "patrick"); Map<Integer, List<String>> grouped = names.stream() .collect(Collectors.groupingBy(String::length)); The output will be: {4=[john, bill], 5=[james, linus], 7=[patrick]}."
Streams can be collected into a List using the toList() terminal operation available in Java 16 and later. Collectors.toSet() collects stream elements into a Set, removing duplicates and foregoing element order. Collectors.toMap(keyMapper, valueMapper) builds a Map where keys and values come from stream elements; collisions require a merge function to resolve duplicate keys. Collectors.joining(delimiter) concatenates stream elements into a single String with a chosen delimiter, for example producing 'BILL, JAMES, PATRICK' after mapping names to uppercase. Collectors.groupingBy(classifier) groups elements into a Map<Key,List<Value>> keyed by the classifier function. Collectors.summarizingInt(mapper) yields IntSummaryStatistics for numeric summaries such as sum, count, min, max, and average.
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