LongStream findFirst() in Java

LongStream findFirst() returns an OptionalLong (a container object which may or may not contain a non-null value) describing the first element of this stream, or an empty OptionalLong if the stream is empty

Syntax :

OptionalLong findFirst()

Parameters :

1. OptionalLong : A container object which may or may not contain a non-null value.

Return Value : The function returns an OptionalLong describing the first element of this stream, or an empty OptionalLong if the stream is empty.

Note : findAny() is a terminal-short-circuiting operation of Stream interface. This method returns any first element satisfying the intermediate operations.

Example 1 : findFirst() method on Long Stream.

// Java code for LongStream findFirst()
// which returns an OptionalLong describing
// first element of the stream, or an
// empty OptionalLong if the stream is empty.
import java.util.*;
import java.util.stream.LongStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an LongStream
        LongStream stream = LongStream.of(6L, 7L, 8L, 9L);

        // Using LongStream findFirst() to return
        // an OptionalLong describing first element
        // of the stream
        OptionalLong answer = stream.findFirst();

        // if the stream is empty, an empty
        // OptionalLong is returned.
        if (answer.isPresent())
            System.out.println(answer.getAsLong());
        else
            System.out.println("no value");
    }
}

Output :

6

Note : If the stream has no encounter order, then any element may be returned.

Example 2 : findFirst() method to return the first element which is divisible by 4.

// Java code for LongStream findFirst()
// which returns an OptionalLong describing
// first element of the stream, or an
// empty OptionalLong if the stream is empty.
import java.util.OptionalLong;
import java.util.stream.LongStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an LongStream
        LongStream stream = LongStream.of(4L, 5L, 8L, 10L, 12L, 16L)
                                .parallel();

        // Using LongStream findFirst().
        // Executing the source code multiple times
        // must return the same result.
        // Every time you will get the same
        // value which is divisible by 4.
        stream = stream.filter(num -> num % 4 == 0);

        OptionalLong answer = stream.findFirst();
        if (answer.isPresent())
            System.out.println(answer.getAsLong());
    }
}

Output :

4