Implement DoubleSupplier Using Lambda and Method Reference in Java

DoubleSupplier interface is a built-in functional interface defined in java.util.function package. This functional interface doesn’t expect any input but produces a double-valued output. DoubleSupplier interface can be used as an assignment target for lambda expression and method reference. This interface contains only one abstract method: getAsDouble().

Syntax

@FunctionalInterface
public interface DoubleSupplier {
   double getAsDouble();
}

Example of Lambda Expression

import java.util.concurrent.ThreadLocalRandom;
import java.util.function.DoubleSupplier;

public class DoubleSupplierLambdaTest {
   public static void main(String args[]) {
      DoubleSupplier getRandomDouble = () -> {    // lambda expression
         double doubleVal = ThreadLocalRandom.current().nextDouble(0000, 9999);
         return Math.round(doubleVal);
      };
      double randomVal = getRandomDouble.getAsDouble();
      System.out.println("Random Double Generated : " + randomVal);
      System.out.println("Random Double Generated : " + getRandomDouble.getAsDouble());
      System.out.println("Random Double Generated : " + getRandomDouble.getAsDouble());
   }
}

Output

Random Double Generated : 4796.0
Random Double Generated : 2319.0
Random Double Generated : 7403.0

Example of Method Reference

import java.util.function.DoubleSupplier;

public class DoubleSupplierMethodRefTest {
   public static void main(String args[]) {
      DoubleSupplier random = Math::random;   // method reference
      for(int i = 0; i < 5; ++i) {
         System.out.println("random number between 1 to 100: " + (random.getAsDouble() * 100) );
      }
   }
}

Output

random number between 1 to 100: 65.72186642095294
random number between 1 to 100: 42.389730890035146
random number between 1 to 100: 16.89589518236835
random number between 1 to 100: 45.85184122201681
random number between 1 to 100: 2.626718898776015