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Java 8 Streams and its operations
Streams are sequences of objects from a source, which support aggregate operations. These were introduced in Java 8.
With Java 8, Collection interface has two methods to generate a Stream.
stream() − Returns a sequential stream considering collection as its source.
parallelStream() − Returns a parallel Stream considering collection as its source.
Some operations on streams are −
sorted − The sorted method is use to sort the stream lexicographically or in ascending order
List id = Arrays.asList("Objects","Classes","Interfaces");
List output = id.stream().sorted().collect(Collectors.toList());map − The map method maps the elements in the collection to other objects according to the Predicate passed as a parameter
List list1= Arrays.asList(1,3,5,7); List finalList = list1.stream().map(a -> a * a * a).collect(Collectors.toList());
filter − The filter method is used to select elements according to the Predicate parameter passed
List id = Arrays.asList(“Classes","Methods","Members");
List output = id.stream().filter(s -> s.startsWith("M")).collect(Collectors.toList());The three operations above are intermediate operations. Now let us have a look at the terminal operations
collect − The collect method returns the outcome of the intermediate operations
List id = Arrays.asList(“Classes","Methods","Members");
List output = id.stream().filter(s -> s.startsWith("M")).collect(Collectors.toList());forEach − This method iterates through every element in the stream
List list1 = Arrays.asList(1,3,5,7); List finalList = list1.stream().map(a ->a * a * a).forEach(b->System.out.println(b));
Let us see an example which illustrates the use of Stream −
Example
import java.util.*;
import java.util.stream.*;
public class Example {
public static void main(String args[]) {
List<Integer> list1 = Arrays.asList(11,22,44,21); //creating an integer list
List<String> id = Arrays.asList("Objects","Classes","Methods");
//creating a String list
// map method
List<Integer> answer = list1.stream().map(x -> x*x).collect(Collectors.toList());
System.out.println(answer);
// filter method
List<String> output = id.stream().filter(x->x.startsWith("M")).collect(Collectors.toList());
System.out.println(output);
}
}Output
[121, 484, 1936, 441] [Methods]
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