Java Double valueOf() example

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In this guide, you will learn about the Double valueOf() method in Java programming and how to use it with an example.

1. Double valueOf() Method Overview

Definition:

The valueOf() method of the Java Double class returns a Double instance representing the specified double value or a String containing a double value.

Syntax:

1. Double Double.valueOf(double d) 
2. Double Double.valueOf(String s) throws NumberFormatException

Parameters:

- double d: The value to be represented as a Double instance.

- String s: The string to be converted into a Double instance.

Key Points:

- It provides an optimized, cache-driven method to retrieve a Double instance (potentially reusing previously cached values for specific number ranges).

- The string-based variant of the method can throw a NumberFormatException if the provided string is not a parsable double.

- Useful for converting both primitive double values and string representations of double values into Double objects.

2. Double valueOf() Method Example

public class ValueOfExample {
    public static void main(String[] args) {
        // Using valueOf with double primitive
        double primitiveValue = 123.45;
        Double doubleObject1 = Double.valueOf(primitiveValue);
        System.out.println("Double object from primitive: " + doubleObject1);

        // Using valueOf with string representation
        String stringValue = "456.78";
        Double doubleObject2 = Double.valueOf(stringValue);
        System.out.println("Double object from string: " + doubleObject2);

        // Exception case (uncomment to see the error)
        // String invalidString = "not a number";
        // Double doubleObject3 = Double.valueOf(invalidString);  // Throws NumberFormatException
    }
}

Output:

Double object from primitive: 123.45
Double object from string: 456.78

Explanation:

In the example provided, we first use the valueOf() method to convert a primitive double value, 123.45, into its Double object representation. 

Subsequently, the string representation of a double value, "456.78", is converted into a Double object. 

A commented-out portion demonstrates the exception that arises when attempting to convert an invalid string into a Double object.

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