Java Guava | Doubles.toArray() method with Examples

The toArray() method of Doubles Class in the Guava library is used to convert the double values, passed as the parameter to this method, into a Double Array. These double values are passed as a Collection to this method. This method returns a Double array.

Syntax:

public static double[] toArray(Collection<? extends Number> collection)

Parameters: This method accepts a mandatory parameter collection which is the collection of double values to be converted in to a Double array.

Return Value: This method returns a double array containing the same values as a collection, in the same order.

Exceptions: This method throws NullPointerException if the passed collection or any of its elements is null.

Below programs illustrate the use of toArray() method:

Example 1 :

// Java code to show implementation of
// Guava's Doubles.toArray() method

import com.google.common.primitives.Doubles;
import java.util.Arrays;
import java.util.List;

class GFG {

    // Driver's code
    public static void main(String[] args)
    {

        // Creating a List of Doubles
        List<Double> myList
            = Arrays.asList(1.2, 2.3, 3.4, 4.5, 5.6);

        // Using Doubles.toArray() method to convert
        // a List or Set of Double to an array of Double
        double[] arr = Doubles.toArray(myList);

        // Displaying an array containing each
        // value of collection,
        // converted to a double value
        System.out.println(Arrays.toString(arr));
    }
}

Output:

[1.2, 2.3, 3.4, 4.5, 5.6]

Example 2 :

// Java code to show implementation of
// Guava's Doubles.toArray() method

import com.google.common.primitives.Doubles;
import java.util.Arrays;
import java.util.List;

class GFG {

    // Driver's code
    public static void main(String[] args)
    {

        try {
            // Creating a List of Doubles
            List<Double> myList
                = Arrays.asList(1.2, 2.3, 3.4, null);

            // Using Doubles.toArray() method
            // to convert a List or Set of Double
            // to an array of Double.
            // This should raise "NullPointerException"
            // as the collection contains "null"
            // as an element
            double[] arr = Doubles.toArray(myList);

            // Displaying an array containing each
            // value of collection,
            // converted to a double value
            System.out.println(Arrays
                                   .toString(arr));
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

Output:

java.lang.NullPointerException

Reference :
https://google.github.io/guava/releases/19.0/api/docs/com/google/common/primitives/Doubles.html#toArray(java.util.Collection)