Find the first element of a Stream in Java

Finding the first element of a stream in Java involves leveraging the Stream API provided by the language. Streams provide a way to process collections of objects in a functional style, allowing operations to be chained together easily.

Examples:

Example 1:

Input: Stream of Strings containing {"apple", "banana", "orange"}

Output: "apple"

Explanation:

Given a stream of strings representing fruits, the findFirst() method returns the first element of the stream, which is "apple".

Example 2:

Input: Stream of Integers containing {10, 20, 30, 40, 50}

Output: 10

Explanation:

In this example, the stream consists of integers. By applying the findFirst() method, the first element of the stream, which is 10, is retrieved.

Example 3:

Input: Empty Stream

Output: "Stream is empty!"

Explanation:

When the stream is empty, invoking the findFirst() method results in an empty optional. Consequently, the program prints a message indicating that the stream is empty.

Approach 1: Using findFirst()

ALGORITHM:

Step 1: Define a Stream of elements using Stream.of() or other stream sources.

Step 2: Create a method findFirstElement that takes a Stream as input.

Step 3: Use the findFirst() method on the stream to get the first element as an Optional.

Step 4: Check if the Optional contains a value using isPresent().

Step 5: Print the first element if present, or indicate that the stream is empty.

Implementation:

The implementation of the above steps given below

FileName: StreamExample1.java

import java.util.Arrays;

import java.util.Optional;

import java.util.stream.Stream;

public class StreamExample1 {

    public static void main(String[] args) {

        // Example 1: Stream of Strings

        Stream stringStream = Stream.of("apple", "banana", "orange");

        findFirstElement(stringStream);

        // Example 2: Stream of Integers

        Stream integerStream = Stream.of(10, 20, 30, 40, 50);

        findFirstElement(integerStream);

        // Example 3: Empty Stream

        Stream

Output:

First element of the stream: apple

First element of the stream: 10

Stream is empty!

Method 2: Using findAny()

ALGORITHM:

Step 1: Define a stream of elements using Stream.of() or other stream sources, such as a stream of Strings or Integers.

Step 2: Create a method findAnyElement that takes a Stream as input, where T is a generic type.

Step 3: Inside the findAnyElement method, use the findAny() method on the input stream to retrieve an Optional containing any element from the stream.

Step 4: Check if the Optional returned by findAny() contains a value using the isPresent() method.

Step 5: If an element is present, retrieve it using get() and print it. If the stream is empty, indicate that the stream is empty.

Implementation:

The implementation of the above steps given below

FileName: StreamExample2.java

import java.util.Optional;

import java.util.stream.Stream;

public class StreamExample2 {

    public static void main(String[] args) {

        // Example 1: Stream of Strings

        Stream stringStream = Stream.of("apple", "banana", "orange");

        findAnyElement(stringStream);

        // Example 2: Stream of Integers

        Stream integerStream = Stream.of(10, 20, 30, 40, 50);

        findAnyElement(integerStream);

        // Example 3: Empty Stream

        Stream

Output:

Any element of the stream: apple

Any element of the stream: 10

Stream is empty!

Method 3: using reduce()

ALGORITHM:

Step 1: Define a stream of elements using Stream.of() or other stream sources.

Step 2: Create a method findFirstElement that takes a Stream as input, where T is a generic type.

Step 3: Inside the findFirstElement method, use the reduce() method on the input stream to retrieve an Optional containing the first element from the stream.

Step 3.1: The reduce() method takes a binary operator that takes two elements and returns the first element, effectively returning the first element of the stream.

Step 4: Check if the Optional returned by reduce() contains a value using the isPresent() method.

Step 5: If an element is present, retrieve it using get() and print it. If the stream is empty, indicate that the stream is empty.

Implementation:

The implementation of the above steps given below

FileName: StreamExample3.java

import java.util.Optional;

import java.util.stream.Stream;

public class StreamExample3 {

    public static void main(String[] args) {

        // Example 1: Stream of Strings

        Stream stringStream = Stream.of("apple", "banana", "orange");

        findFirstElement(stringStream);

        // Example 2: Stream of Integers

        Stream integerStream = Stream.of(10, 20, 30, 40, 50);

        findFirstElement(integerStream);

        // Example 3: Empty Stream

        Stream

Output:

First element of the stream: apple

First element of the stream: 10

Stream is empty!