Stream In Java8

Introduced in Java 8, the Stream API is used to process collections of objects. A stream is a sequence of objects that supports various methods which can be pipe lined to produce the desired result. The features of Java stream are –

• 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, they only provide the result as per the pipe lined methods.
• Each intermediate operation is lazily executed and returns a stream as a result, hence various intermediate operations can be pipe lined. Terminal operations mark the end of the stream and return the result.

Different Operations On Streams-
Intermediate Operations:

1. map: The map method is used to map the items in the collection to other objects according to the Predicate passed as argument.
   List number = Arrays.asList(2,3,4,5);
List square = number.stream().map(x->x*x).collect(Collectors.toList());
2. filter: The filter method is used to select elements as per the Predicate passed as argument.
   List names = Arrays.asList("Reflection","Collection","Stream");
List result = names.stream().filter(s->s.startsWith("S")).collect(Collectors.toList());
3. sorted: The sorted method is used to sort the stream.
   List names = Arrays.asList("Reflection","Collection","Stream");
List result = names.stream().sorted().collect(Collectors.toList());

Terminal Operations:

1. collect: The collect method is used to return the result of the intermediate operations performed on the stream.
   List number = Arrays.asList(2,3,4,5,3);
Set square = number.stream().map(x->x*x).collect(Collectors.toSet());
2. forEach: The forEach method is used to iterate through every element of the stream.
   List number = Arrays.asList(2,3,4,5);
number.stream().map(x->x*x).forEach(y->System.out.println(y));
3. reduce: The reduce method is used to reduce the elements of a stream to a single value.
   The reduce method takes a BinaryOperator as a parameter.List number = Arrays.asList(2,3,4,5);
int even = number.stream().filter(x->x%2==0).reduce(0,(ans,i)-> ans+i);
   Here ans variable is assigned 0 as the initial value and i is added to it .

Program to demonstrate the use of Stream

//a simple program to demonstrate the use of stream in java import java.util.*; import java.util.stream.*;   class Demo {   public static void main(String args[])   {       // create a list of integers     List<Integer> number = Arrays.asList(2,3,4,5);       // demonstration of map method     List<Integer> square = number.stream().map(x -> x*x).                            collect(Collectors.toList());     System.out.println(square);       // create a list of String     List<String> names =                 Arrays.asList("Reflection","Collection","Stream");       // demonstration of filter method     List<String> result = names.stream().filter(s->s.startsWith("S")).                           collect(Collectors.toList());     System.out.println(result);       // demonstration of sorted method     List<String> show =             names.stream().sorted().collect(Collectors.toList());     System.out.println(show);       // create a list of integers     List<Integer> numbers = Arrays.asList(2,3,4,5,2);       // collect method returns a set     Set<Integer> squareSet =          numbers.stream().map(x->x*x).collect(Collectors.toSet());     System.out.println(squareSet);       // demonstration of forEach method     number.stream().map(x->x*x).forEach(y->System.out.println(y));       // demonstration of reduce method     int even =        number.stream().filter(x->x%2==0).reduce(0,(ans,i)-> ans+i);       System.out.println(even);   } }

You can download the source code from here:https://github.com/jagroopbhanot/letsLearn.git