JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

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How Java 8 Streams work?


Streams support functional-style operations on streams of elements, such as map-reduce transformations on collections. Stream operations are divided into intermediate and terminal operations, and are combined to form stream pipelines. A stream pipeline consists of a source (such as a Collection, an array, a generator function, or an I/O channel); followed by zero or more intermediate operations such as Stream.filter or Stream.map; and a terminal operation such as Stream.forEach or Stream.reduce.

Intermediate operations return a new stream. They are always lazy; executing an intermediate operation such as filter() does not actually perform any filtering, but instead creates a new stream that, when traversed, contains the elements of the initial stream that match the given predicate. Traversal of the pipeline source does not begin until the terminal operation of the pipeline is executed.

Terminal operations, such as Stream.forEach or IntStream.sum, may traverse the stream to produce a result or a side-effect. After the terminal operation is performed, the stream pipeline is considered consumed, and can no longer be used; if you need to traverse the same data source again, you must return to the data source to get a new stream. In almost all cases, terminal operations are eager, completing their traversal of the data source and processing of the pipeline before returning. Only the terminal operations iterator() and spliterator() are not; these are provided as an "escape hatch" to enable arbitrary client-controlled pipeline traversals in the event that the existing operations are not sufficient to the task.

Intermediate operations are further divided into stateless and stateful operations. Stateless operations, such as filter and map, retain no state from previously seen element when processing a new element -- each element can be processed independently of operations on other elements. Stateful operations, such as distinct and sorted, may incorporate state from previously seen elements when processing new elements.

Stateful operations may need to process the entire input before producing a result. For example, one cannot produce any results from sorting a stream until one has seen all elements of the stream. As a result, under parallel computation, some pipelines containing stateful intermediate operations may require multiple passes on the data or may need to buffer significant data. Pipelines containing exclusively stateless intermediate operations can be processed in a single pass, whether sequential or parallel, with minimal data buffering.

Here is a simple example on Steam operations and pipelines: The below example, combines filtering a list based on number of characters, converting them to upper case, sorting and finally printing them into single line of code, which is the power of streams.

package com.java2novice.streams;

import java.util.Arrays;
import java.util.List;

public class StreamExample {

	public static void main(String a[]) {

		List<String> vechicles = Arrays.asList("bus", "car", "bicycle", "flight", "train");

		vechicles.stream().filter(str->str.length() > 3).map(String::toUpperCase).sorted().forEach(System.out::println);;
	}
}

Output:
BICYCLE
FLIGHT
TRAIN
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Java 8 Streams Examples

  1. How Java 8 Streams work?
  2. Java 8 Streams parallelism introduction.
  3. Explain non-interference behavior of Java 8 Streams.
  4. Create Java 8 Stream using Stream.of() method example.
  5. Create Java 8 Stream using List example.
  6. Create Java 8 Stream using Stream.generate() method.
  7. Java 8 Stream.filter() example.
  8. Java 8 Stream.map() example.
  9. Java 8 Stream flatmap method example.
  10. Java 8 Stream peek method example.
  11. Java 8 Stream distinct method example.
  12. Java 8 Stream sorted method example.
  13. Java 8 Stream limit method example.
  14. Java 8 Stream forEach method example.
  15. Java 8 Stream toArray method example.
  16. Java 8 Stream reduce method example.
  17. Java 8 Stream collect method example.
  18. Java 8 Stream concat method example.
  19. Java 8 Stream anyMatch(), allMatch() and noneMatch() example.
  20. Java 8 Stream findFirst(), findAny() example.
  21. Primitive type Stream example.
Knowledge Centre
When to use LinkedList or ArrayList?
Accessing elements are faster with ArrayList, because it is index based. But accessing is difficult with LinkedList. It is slow access. This is to access any element, you need to navigate through the elements one by one. But insertion and deletion is much faster with LinkedList, because if you know the node, just change the pointers before or after nodes. Insertion and deletion is slow with ArrayList, this is because, during these operations ArrayList need to adjust the indexes according to deletion or insetion if you are performing on middle indexes. Means, an ArrayList having 10 elements, if you are inserting at index 5, then you need to shift the indexes above 5 to one more.
Famous Quotations
Insanity: doing the same thing over and over again and expecting different results.
-- Albert Einstein

About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java™ Platform Standard Ed. 8 - API Specification | Java is registered trademark of Oracle.
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