First of all, Java 8 Streams should not be confuses with Java I/O streams. The Stream API is use to process collections of objects. Java provides a new additional package in Java 8 called java.util.stream. In stream one or more operations can be perform. The Streams operations are either intermediate or terminal.
Stream provides following features:
- The stream does not store elements.
- A stream is not a data structure instead it takes input from the Collections, Arrays or I/O channels.
- Streams don’t change the original data structure.
- Stream is lazy and evaluates code only when required.
- The elements of a stream are only visited once during the life of a stream.
Stream Operations
Streams abstraction has a long list of useful functions. They are divided into intermediate operations (return Stream<T>) and terminal operations (return a result of definite type). Let us have a look on some of the stream operations.
Streams Intermediate Operations
Intermediate operations return the stream itself so you can chain multiple methods calls in a row.
Filter
The filter() method accepts a Predicate to filter all elements of the stream.
Example :
List<String> names = Arrays.asList("Java","Rust","DevOps");
List<String> result = names.stream().filter(s -> s.startsWith("J"))
.collect(Collectors.toList());
result.forEach(System.out::println);Output :
Map
The map() method is used to returns a stream consisting of the results of applying the given function to the elements of this stream.
Example :
List<String> number = Arrays.asList(2,3,4,5);
List<String> square = number.stream().map(x->x*x).collect(Collectors.toList());
square.forEach(System.out::println);Output :
Sorted
The sorted() method is an intermediate operation that returns a sorted view of the stream.
Example :
List<String> names = Arrays.asList("Java","Rust","DevOps");
List<String> result = names.stream().sorted().collect(Collectors.toList());
result.forEach(System.out::println);Output :
Streams Terminal Operations
Terminal operations return a result of a certain type after processing all the stream elements.
Collect
The collect() method is used to receive elements from a steam and store them in a collection.
Example :
List<Integer> number = Arrays.asList(2,3,4,5,3);
Set<Integer> square = number.stream().map(x->x*x).collect(Collectors.toSet());
square.forEach(System.out::println);Output :
forEach
The forEach() method is used to iterate through every element of the stream.
Example :
List<Integer> number = Arrays.asList(2,3,4,5);
number.stream().map(x->x*x).forEach(y->System.out.println(y));Output :
Reduce
The reduce() method takes a sequence of input elements and combines them into a single summary result by repeated operation.
Example :
List<Integer> number = Arrays.asList(2,3,4,5);
int even = number.stream().filter(x->x%2==0).reduce(0, Integer::sum);
System.out.println(even);Output :
Thanks for Reading !!
