Collecting elements with streams

Stream<T> stream = collection.stream();
// Collect to a result
R result = stream.collect(Collectors.someCollector());Code language: JavaScript (javascript)

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
List<String> filteredNames = names.stream()
    .filter(name -> name.startsWith("A"))
    .collect(Collectors.toList());
// Result: [Alice]Code language: JavaScript (javascript)

 Collect to a Set

List<String> names = Arrays.asList("Alice", "Bob", "Alice");
Set<String> uniqueNames = names.stream()
    .collect(Collectors.toSet());
// Result: [Alice, Bob] (duplicates removed)Code language: JavaScript (javascript)

  Collect to a Map

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
Map<String, Integer> nameLengthMap = names.stream()
    .collect(Collectors.toMap(
        name -> name,           // Key: the name itself
        name -> name.length()   // Value: length of the name
    ));
// Result: {Alice=5, Bob=3, Charlie=7}Code language: JavaScript (javascript)

  Joining Strings

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
String result = names.stream()
    .collect(Collectors.joining(", "));
// Result: Alice, Bob, CharlieCode language: JavaScript (javascript)

  Grouping Elements

List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");
Map<Integer, List<String>> namesByLength = names.stream()
    .collect(Collectors.groupingBy(String::length));
// Result: {3=[Bob], 5=[Alice], 6=[David], 7=[Charlie]}Code language: JavaScript (javascript)

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
Map<Boolean, List<String>> longNames = names.stream()
    .collect(Collectors.partitioningBy(name -> name.length() > 3));
// Result: {false=[Bob], true=[Alice, Charlie]}Code language: JavaScript (javascript)

  Partitioning Elements

List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
LinkedList<String> linkedList = names.stream()
    .collect(Collectors.toCollection(LinkedList::new));
// Result: LinkedList containing [Alice, Bob, Charlie]Code language: JavaScript (javascript)

 Custom Collection Use toCollection() to collect into a specific collection type

Collecting elements with streams in Java provides a versatile mechanism for aggregating data into different types of collections or structures, making it a powerful tool for data manipulation and aggregation tasks in Java programming.