This concept was added to Java 8. Support functional-style operations on streams of elements, such as map-reduce transformations on collections.
What is Stream?
Stream is an immutable flow of elements, you could compare the way the streams process content to a loop.
Package java.util.stream;
Stream operations are divided into intermediate and terminal operations. A stream source can be a Collection, an array, a generator function.
Intermediate operations
The intermediate operations are lazy operations and return a new stream. Some examples at continuous:
- anyMatch()
- distinct()
- filter()
- findFirst()
- flatmap()
- map()
- skip()
- sorted()
- peek()
- limit()
Terminal operations
The terminal operations terminate the stream source pipeline after performing the operations.
- count()
- max()
- min()
- reduce()
- summaryStatistics()
- forEach()
- forEachOrdered()
- sum()
- toArray()
- collect()
- anyMatch
- allMatch()
- noneMatch()
- findAny()
- findFirst()
We can create stream via the stream() and parallelStream() methods and from an array via Arrays.stream(Object[]) method.
| Interface | Description |
|---|---|
| BaseStream> | Base interface for streams, which are sequences of elements supporting sequential and parallel aggregate operations. |
| Collector | A mutable reduction operation that accumulates input elements into a mutable result container, optionally transforming the accumulated result into a final representation after all input elements have been processed. |
| DoubleStream | A sequence of primitive double-valued elements supporting sequential and parallel aggregate operations. |
| DoubleStream.Builder | A mutable builder for a DoubleStream. |
| IntStream | A sequence of primitive int-valued elements supporting sequential and parallel aggregate operations. |
| IntStream.Builder | A mutable builder for an IntStream. |
| LongStream | A sequence of primitive long-valued elements supporting sequential and parallel aggregate operations. |
| LongStream.Builder | A mutable builder for a LongStream. |
| Stream | A sequence of elements supporting sequential and parallel aggregate operations. |
| Stream.Builder | A mutable builder for a Stream. |
We can use these classes to collect the intermediate data and manipulate the stream.
| Class | Description |
|---|---|
| Collectors | |
| Implementations of Collector that implement various useful reduction operations, such as accumulating elements into collections, summarizing elements according to various criteria, etc. | |
| StreamSupport | Low-level utility methods for creating and manipulating streams. |
Example
IntStream
.range(1, 10)
.forEach(System.out::print);
System.out.println();
[1,2,3,4,5,6,7,8,9]
Intermediate
Stream.of(18, 22, 5, 7, 14, 17, 33)
.filter(x -> x > 18)
.forEach(System.out::print);
[22,33]
Terminal
System.out.println("Min: " + IntStream.of(18, 22, 5, 7, 14, 17, 33).min());
System.out.println("Max: " + IntStream.of(18, 22, 5, 7, 14, 17, 33).max());
System.out.println("Count, Size, or Length: " + IntStream.of(18, 22, 5, 7, 14, 17, 33).count());
System.out.println("Sum: " + IntStream.of(18, 22, 5, 7, 14, 17, 33).sum());
[Min: OptionalInt[5]]
[Max: OptionalInt[33]]
[Count, Size, or Length: 7]
[Sum: 116]
Stream.of(18, 22, 5, 7, 14, 17, 33, 5, 22)
.collect(Collectors.toSet())
.forEach(System.out::println);
[17,33,18,5,22,7,14,2]
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