Convert String to Double in Java

In this article, we will learn to convert string to double in Java. String to double is a very common need when dealing with user inputs, files, and APIs. There are several ways through which this process can be done in Java.

Problem Statement

Given a string representing a decimal number, convert it into a double in Java. The input string is guaranteed to be a valid numeric representation.

For example
Input

String str = "23.6";

Output

23.6

Different Approaches

The following are the two different approaches for converting string to double in Java ?

• Using Double.parseDouble()
• Using Double.valueOf()

Using Double.parseDouble()

The Double.parseDouble() method is the most commonly used way to convert a string to a double. It belongs to the Double wrapper class and is efficient.

Converting the string to double using parseDouble() in Java ?

double res = Double.parseDouble("23.6");

Example

Below is an example of converting string to double using parseDouble() ?

public class Demo {
   public static void main(String args[]){
      String str = "23.6";
      double res = Double.parseDouble(str);
      System.out.println("Double (String to Double) = "+res);
   }
}

Output

Double (String to Double) = 23.6

Time Complexity: O(1), as the conversion operation takes constant time.
Space Complexity: O(1), since no additional memory is allocated apart from storing the result.

Using Double.valueOf()

The Double.valueOf() method also converts a String to a double, but it returns an instance of double instead of a primitive double.

Converting the string to double using valueOf() in Java ?

Double numObj = Double.valueOf(numberStr);

Example

Below is an example of converting string to double using valueOf() ?

public class Main {
    public static void main(String[] args) {
        String numberStr = "99.99";
        Double numObj = Double.valueOf(numberStr);
        double num = numObj; // Unboxing
        System.out.println("Converted double: " + num);
    }
}

Output

Converted double: 99.99

Time Complexity: O(1), as the conversion operation takes constant time.
Space Complexity: O(1), since no additional memory is allocated apart from storing the result.

Conclusion

Converting a String to a double in Java is straightforward using Double.parseDouble() or Double.valueOf(). Both methods provide efficient ways to handle numerical string conversions. While parseDouble() returns a primitive double, valueOf() returns a Double object, making it useful when working with collections.