Java 8 | DoubleSupplier Interface with Examples

The DoubleSupplier interface is a specialized functional interface introduced in Java 8 and available in the java.util.function package. It represents a supplier of double values and does not accept any input arguments. It is commonly used when a double value needs to be generated, computed, or supplied on demand.

• Primitive specialization of Supplier<Double>.
• Avoids boxing and unboxing overhead.
• Supports lambda expressions and method references.

import java.util.function.DoubleSupplier;

public class Main {
    public static void main(String[] args) {

        DoubleSupplier randomValue =
            () -> Math.random();

        System.out.println(randomValue.getAsDouble());
    }
}

0.08957323531712014

Explanation: In this example, the DoubleSupplier generates a random double value using Math.random(). The getAsDouble() method is used to retrieve the generated value.

Syntax

@FunctionalInterface
public interface DoubleSupplier

Methods of DoubleSupplier Interface

1. getAsDouble() Method

The getAsDouble() method is the functional method of the DoubleSupplier interface. It does not take any arguments and returns a double value.

• Returns a primitive double value.
• Does not accept any input parameters.

Syntax:

double getAsDouble()

Return Value: Returns a double value.

import java.util.function.DoubleSupplier;

public class Main {
    public static void main(String[] args) {

        DoubleSupplier random =
            () -> Math.random();

        System.out.println(random.getAsDouble());
    }
}

0.7888683342937106

Explanation: The DoubleSupplier generates and returns a random double value between 0.0 and 1.0 each time getAsDouble() is called.

Example 2: Return Circle Area

import java.util.function.DoubleSupplier;

public class Main {
    public static void main(String[] args) {

        double radius = 5.0;

        DoubleSupplier area =
            () -> 3.14 * radius * radius;

        System.out.println(area.getAsDouble());
    }
}

78.5

Explanation: The supplier calculates the area of a circle using a predefined radius and returns the result as a double value.

DoubleSupplier vs Supplier<Double>

Advantages of DoubleSupplier

• Avoids boxing and unboxing of Double objects.
• Improves performance when working with primitive double values.
• Useful for generating random numbers and calculated values.
• Supports lambda expressions and method references.
• Simplifies code in functional programming.