How to convert int to double in Java?

Converting Int to Double in Java: A Step-by-Step Guide

Introduction

In Java, converting an integer to a double is a common operation that can be performed using various methods. This article will provide a comprehensive guide on how to convert an integer to a double in Java, including the most common methods and scenarios.

Method 1: Using the Double.parseDouble() Method

The Double.parseDouble() method is a built-in method in Java that can convert an integer to a double. Here’s how to use it:

• Syntax: Double.parseDouble(String s)
• Parameters: String s – the string representation of the integer to be converted
• Return Value: double – the converted double value

Here’s an example:

public class Main {

    public static void main(String[] args) {

        int num = 10;

        double doubleNum = Double.parseDouble(String.valueOf(num));

        System.out.println("Double of " + num + " is " + doubleNum);

    }

}

Method 2: Using the Double.valueOf() Method

The Double.valueOf() method is another built-in method in Java that can convert an integer to a double. Here’s how to use it:

• Syntax: Double.valueOf(String s)
• Parameters: String s – the string representation of the integer to be converted
• Return Value: double – the converted double value

Here’s an example:

public class Main {

    public static void main(String[] args) {

        int num = 10;

        double doubleNum = Double.valueOf(String.valueOf(num));

        System.out.println("Double of " + num + " is " + doubleNum);

    }

}

Method 3: Using a Custom Conversion Method

You can also create a custom conversion method to convert an integer to a double. Here’s an example:

public class Main {

    public static void main(String[] args) {

        int num = 10;

        double doubleNum = convertToIntToDouble(num);

        System.out.println("Double of " + num + " is " + doubleNum);

    }



    public static double convertToIntToDouble(int num) {

        return (double) num;

    }

}

Method 4: Using a Third-Party Library

There are also third-party libraries available that provide methods to convert integers to doubles. Here’s an example using the java.math.BigInteger class:

import java.math.BigInteger;



public class Main {

    public static void main(String[] args) {

        int num = 10;

        double doubleNum = new BigInteger(String.valueOf(num)).doubleValue();

        System.out.println("Double of " + num + " is " + doubleNum);

    }

}

Method 5: Using a Custom Class

You can also create a custom class to represent the integer and double values. Here’s an example:

public class Main {

    public static void main(String[] args) {

        int num = 10;

        double doubleNum = convertToIntToDouble(num);

        System.out.println("Double of " + num + " is " + doubleNum);

    }



    public static double convertToIntToDouble(int num) {

        return num;

    }

}

Method 6: Using a Third-Party Library (continued)

There are also third-party libraries available that provide methods to convert integers to doubles. Here’s an example using the org.apache.commons.math3 library:

import org.apache.commons.math3.util.FastMath;



public class Main {

    public static void main(String[] args) {

        int num = 10;

        double doubleNum = new FastMath().doubleValue(num);

        System.out.println("Double of " + num + " is " + doubleNum);

    }

}

Conclusion

Converting an integer to a double in Java is a common operation that can be performed using various methods. The Double.parseDouble() method is a built-in method that can be used to convert an integer to a double. You can also create a custom conversion method, use a third-party library, or create a custom class to represent the integer and double values. The choice of method depends on the specific requirements of your application.

Table: Converting Int to Double Methods

Method	Syntax	Parameters	Return Value
Double.parseDouble(String s)	Double.parseDouble(String s)	String s	double
Double.valueOf(String s)	Double.valueOf(String s)	String s	double
Custom Conversion Method	public static double convertToIntToDouble(int num)	int num	double
Third-Party Library	import java.math.BigInteger;	int num	double
Custom Class	public class Main {	int num	double
Third-Party Library (continued)	import org.apache.commons.math3.util.FastMath;	int num	double

Important Notes

• The Double.parseDouble() method can throw a NumberFormatException if the input string is not a valid double representation.
• The Double.valueOf() method can throw a NumberFormatException if the input string is not a valid double representation.
• The custom conversion method and third-party library methods may have different behavior or performance characteristics compared to the built-in methods.
• The custom class method may have different behavior or performance characteristics compared to the built-in methods.