DoubleStream findFirst() with examples

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

Syntax :

OptionalDouble findFirst()

Parameters :

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

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

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

Example 1 : findFirst() method on Double Stream.

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

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an DoubleStream
        DoubleStream stream = DoubleStream.of(6.2, 7.3, 8.4, 9.5);

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

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

Output :

6.2

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 DoubleStream findFirst()
// which returns an OptionalDouble describing
// first element of the stream, or an
// empty OptionalDouble if the stream is empty.
import java.util.OptionalDouble;
import java.util.stream.DoubleStream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // Creating an DoubleStream
        DoubleStream stream = DoubleStream.of(4.7, 4.5,
                    8.0, 10.2, 12.0, 16.0).parallel();

        // Using DoubleStream findFirst().
        // Executing the source code multiple times
        // must return the same result.
        // Every time you will get the same
        // Double value which is divisible by 4.
        stream = stream.filter(num -> num % 4.0 == 0);

        OptionalDouble answer = stream.findFirst();
        if (answer.isPresent())
            System.out.println(answer.getAsDouble());
    }
}

Output :

8.0