The java.util.stream.Collectors class provides various useful reduction operations, such as accumulating elements into collections, summarizing elements according to various criteria, etc.
Java Collectors Methods
The table below contains common methods of the Java Collectors class, each with a link to a detailed explanation, examples, and real-world uses. Click on the method names to learn more about how to use them effectively in your applications.
| Method | Description |
|---|---|
| counting() | Returns a collector that counts the number of input elements. |
| averagingInt() | Returns a collector that computes the arithmetic mean of an integer-valued function applied to the input elements. |
| collectingAndThen() | Adapts a collector to perform an additional finishing transformation. |
| filtering() | Returns a collector that filters the input elements using a predicate before accumulating them. |
| flatMapping() | Returns a collector that flattens the input elements using a mapping function before accumulating them. |
| groupingBy() | Returns a collector that groups the input elements by a classifier function. |
| groupingByConcurrent() | Returns a concurrent collector that groups the input elements by a classifier function. |
| joining() | Returns a collector that concatenates the input elements into a single string. |
| mapping() | Returns a collector that applies a mapping function to the input elements before accumulating them. |
| maxBy() | Returns a collector that finds the maximum element according to a comparator. |
| minBy() | Returns a collector that finds the minimum element according to a comparator. |
| partitioningBy() | Returns a collector that partitions the input elements according to a predicate. |
| reducing() | Returns a collector that performs a reduction on the input elements. |
| summarizingDouble() | Returns a collector that computes the summary statistics for a double-valued function applied to the input elements. |
| summarizingInt() | Returns a collector that computes the summary statistics for an integer-valued function applied to the input elements. |
| summingDouble() | Returns a collector that computes the sum of a double-valued function applied to the input elements. |
| teeing() | Returns a collector that passes the input elements to two other collectors and then merges their results. |
| toCollection() | Returns a collector that accumulates the input elements into a new collection. |
| toConcurrentMap() | Returns a concurrent collector that accumulates the input elements into a map. |
| toList() | Returns a collector that accumulates the input elements into a new list. |
| toMap() | Returns a collector that accumulates the input elements into a map. |
| toSet() | Returns a collector that accumulates the input elements into a new set. |
| toUnmodifiableList() | Returns a collector that accumulates the input elements into an unmodifiable list. |
| toUnmodifiableMap() | Returns a collector that accumulates the input elements into an unmodifiable map. |
| toUnmodifiableSet() | Returns a collector that accumulates the input elements into an unmodifiable set. |
In conclusion, the java.util.stream.Collectors class provides a variety of methods to perform reduction operations on streams. These methods offer flexibility in processing and collecting stream elements into various data structures. For more detailed information, refer to the official Java Documentation.