Java Streams

Stream: - It is an API introduced in Java 8 used to process a collection of objects. It primarily has two types of operations: -

• Intermediate Operations
• Terminal Operations

It is a combination of one or more intermediate operations followed by a terminal operation. Each intermediate operation is lazily executed and returns a stream as a result, hence, various intermediate operations can be pipelined. Terminal operations mark the end of the stream and return the result.

Some common intermediate and terminal operations are as follows: -

1. map: - It is an intermediate operation used to return a stream consisting of the results of applying the given function to the elements of this stream.

JAVA
1<R> Stream<R> map(Function<? super T, ? extends R> mapper)

2. filter: - This intermediate operation is used to select elements as per the Predicate passed as an argument.

JAVA
1Stream<T> filter(Predicate<? super T> predicate)

3. sorted: - It is an intermediate operation used to sort the stream.

JAVA
1Stream<T> sorted()
2Stream<T> sorted(Comparator<? super T> comparator)

4. collect: - It is a terminal operation used to collect the output of intermediate operations and return the result.

JAVA
1<R, A> R collect(Collector<? super T, A, R> collector)

Sample code depicting the usage of above operations: -

JAVA
1import java.util.*;
2import java.util.stream.Collectors;
3
4public class SampleStreamOperations{
5    public static void main(String[] args) {
6        // Sample data
7        List<String> names = Arrays.asList(
8            "Reflection", "Collection", "Stream",
9            "Structure", "Sorting", "State"
10        );
11
12        // forEach: Print each name
13        System.out.println("forEach:");
14        names.stream().forEach(System.out::println);
15
16        // collect: Collect names starting with 'S' into a list
17        List<String> sNames = names.stream().filter(name -> name.startsWith("S")).collect(Collectors.toList());
18        System.out.println("\ncollect (names starting with 'S'):");
19        sNames.forEach(System.out::println);
20
21        // reduce: Concatenate all names into a single string
22        String concatenatedNames = names.stream().reduce(
23            "",
24            (partialString, element) -> partialString + " " + element
25        );
26        System.out.println("\nreduce (concatenated names):");
27        System.out.println(concatenatedNames.trim());
28
29        // count: Count the number of names
30        long count = names.stream().count();
31        System.out.println("\ncount:");
32        System.out.println(count);
33
34        // findFirst: Find the first name
35        Optional<String> firstName = names.stream().findFirst();
36        System.out.println("\nfindFirst:");
37        firstName.ifPresent(System.out::println);
38
39        // allMatch: Check if all names start with 'S'
40        boolean allStartWithS = names.stream().allMatch(name-> name.startsWith("s"));
41        System.out.println("\nallMatch (all start with 'S'):");
42        System.out.println(allStartWithS);
43
44        // anyMatch: Check if any name starts with 'S'
45        boolean anyStartWithS = names.stream().anyMatch(
46            name -> name.startsWith("S")
47        );
48        System.out.println("\nanyMatch (any start with 'S'):");
49        System.out.println(anyStartWithS);
50    }
51}