Java DoubleFunction

Introduction

In Java, the DoubleFunction interface is a functional interface that represents a function that accepts a double-valued argument and produces a result. It is part of the java.util.function package and is commonly used for transforming or processing double values into another type.

Table of Contents

1. What is DoubleFunction?
2. Methods and Syntax
3. Examples of DoubleFunction
4. Real-World Use Case
5. Conclusion

1. What is DoubleFunction?

DoubleFunction is a functional interface that takes a double as an input and returns a result of a specified type. It is useful for operations where a double needs to be converted or processed into another form.

2. Methods and Syntax

The main method in the DoubleFunction interface is:

• R apply(double value): Applies this function to the given argument and returns a result.

Syntax

DoubleFunction<R> doubleFunction = (double value) -> {
    // operation on value
    return result;
};

3. Examples of DoubleFunction

Example 1: Converting Double to String

import java.util.function.DoubleFunction;

public class DoubleToStringExample {
    public static void main(String[] args) {
        // Define a DoubleFunction that converts a double to a string
        DoubleFunction<String> doubleToString = (value) -> "Value: " + value;

        String result = doubleToString.apply(10.5);

        System.out.println(result);
    }
}

Output:

Value: 10.5

Example 2: Calculating the Square

import java.util.function.DoubleFunction;

public class SquareCalculator {
    public static void main(String[] args) {
        // Define a DoubleFunction that calculates the square of a double
        DoubleFunction<Double> square = (value) -> value * value;

        double result = square.apply(4.0);

        System.out.println("Square: " + result);
    }
}

Output:

Square: 16.0

4. Real-World Use Case: Formatting Currency

In financial applications, DoubleFunction can be used to format a double value representing money into a currency string.

import java.util.function.DoubleFunction;
import java.text.NumberFormat;
import java.util.Locale;

public class CurrencyFormatter {
    public static void main(String[] args) {
        // Define a DoubleFunction to format a double as currency
        DoubleFunction<String> formatCurrency = (value) -> {
            NumberFormat currencyFormat = NumberFormat.getCurrencyInstance(Locale.US);
            return currencyFormat.format(value);
        };

        String formattedAmount = formatCurrency.apply(1234.56);

        System.out.println("Formatted Amount: " + formattedAmount);
    }
}

Output:

Formatted Amount: $1,234.56

Conclusion

The DoubleFunction interface is used in Java for transforming double values into other types. It is particularly useful in scenarios where data conversion or processing is required, such as formatting or calculations. Using DoubleFunction can lead to more readable and maintainable code, especially in functional programming.