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A new additional package in Java 8, known as java.util.stream has been added for the users for an efficient programming experience. A stream can be defined as a sequence of objects, supporting multiple methods. In this article we would be exploring Stream in Java
Following pointers will be Covered in this Article,
Before we get started with this article on Stream In Java, let us take a look at some important features,
Moving on with this article on Stream in Java
Streams can be generated by the following methods:
List<String> strings = Arrays.asList("Hello", "", "Hi", "Hola", "Bonjour","", "Namaste"); List<String> filtered = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.toList());
Moving on with this article on Stream in Java
map
The elements present in the collection can be mapped to other objects according to the predicate passed as the argument. The following example is used to display unique squares of the numbers by using the map method.
List<Integer> num = Arrays.asList(5,4,4,2,3,3); List<Integer> squares = num.stream().map( y -> y*y).distinct().collect(Collectors.toList());
filter
Elements can be removed on the basis of a criteria by using this method.
List name = Arrays.asList("Saturday","Sunday","Thursday"); List res = name.stream().filter(s->s.startsWith("S")).collect(Collectors.toList());
sorted
The stream can be sorted by using this method.
List name = Arrays.asList("Saturday","Sunday","Thursday"); List res = name.stream().sorted().collect(Collectors.toList());
collect
The result of processing on the elements of a stream can be combined by using the collect operation.
List num = Arrays.asList(4,3,2,5,6); Set res = num.stream().map(y->y*y).collect(Collectors.toSet());
forEach
This method is used for iterating through every element present in the stream.
List num = Arrays.asList(4,3,2,5); num.stream().map(x->x*x).forEach(y->System.out.println(y));
reduce
The elements of the stream can be reduced to a single value by using this method.
List num = Arrays.asList(4,3,2,5); int even = num.stream().filter(x->x%2==0).reduce(0,(res,i)-> res+i);
The variable res is assigned the value 0 initially, and i is added to it.
Moving on with this article on Stream in Java
The code can be filtered by using the stream method. In the following example, the price of the instruments gets filtered out.
import java.util.*; import java.util.stream.Collectors; class Instrument{ int num; String name; float price; public Instrument(int num, String name, float price) { this.num = num; this.name = name; this.price = price; } } public class Test { public static void main(String[] args) { List<Instrument> instrumentsList = new ArrayList<Instrument>(); //Adding Products instrumentsList.add(new Instrument(1,"Guitar",15000f)); instrumentsList.add(new Instrument(2,"Piano",18000f)); instrumentsList.add(new Instrument(3,"Flute",15000f)); instrumentsList.add(new Instrument(4,"Drums",48000f)); instrumentsList.add(new Instrument(5," Ukulele",32000f)); List<Float> InstrumentPriceList2 =instrumentsList.stream() .filter(p -> p.price > 30000)// filtering data .map(p->p.price)//fetching price .collect(Collectors.toList()); // collecting as list System.out.println(InstrumentPriceList2); } }
Output:
[48000.0, 32000.0]
Moving on with this article on Stream in Java
Iteration can be performed by using stream in java.
import java.util.stream.*; public class Test { public static void main(String[] args){ Stream.iterate(1, element->element+1) .filter(element->element%4==0) .limit(6) .forEach(System.out::println); } }
Output:
4
8
12
16
20
24
Let’s take a look at another example, to understand the concept of Stream in java more effectively.
Example:
import java.util.*; import java.util.stream.*; public class Test { public static void main(String args[]) { //creating a list of integers List<Integer> num = Arrays.asList(6,7,8,9); //using map method List<Integer> squares = num.stream().map(y -> y*y). collect(Collectors.toList()); System.out.println(squares); //creating a list of String List<String> days = Arrays.asList("Friday","Saturday","Sunday"); //filter method List<String> res = days.stream().filter(s->s.startsWith("S")). collect(Collectors.toList()); System.out.println(res); //sorted method List<String> display = days.stream().sorted().collect(Collectors.toList()); System.out.println(display); //creating a list of integers List<Integer> number = Arrays.asList(6,9,5,7,1); //collect method returns a set Set<Integer> sqSet = number.stream().map(y->y*y).collect(Collectors.toSet()); System.out.println(sqSet); //forEach method num.stream().map(y->y*y).forEach(x->System.out.println(x)); //reduce method int even = num.stream().filter(x->x%2==0).reduce(0,(result,i)-> result+i); System.out.println(even); } }
Output:
[36, 49, 64, 81]
[Saturday, Sunday]
[Friday, Saturday, Sunday]
[81, 49, 1, 36, 25]
36
49
64
81
14
Streams enable the user to perform operations on the elements effectually.
Thus we have come to an end of this article on ‘Stream in Java’. If you wish to learn more, check out the Java Training by Edureka, a trusted online learning company. Edureka’s Java J2EE and SOA training and certification course is designed to train you for both core and advanced Java concepts along with various Java frameworks like Hibernate & Spring.
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