Example 1: Java Program to Convert string to double using parseDouble()

class Main{
  public static void main(String[] args){

    // create string variables
    String str1 = "23";
    String str2 = "456.6";

    // convert string to double
    // using parseDouble()
    double num1 = Double.parseDouble(str1);
    double num2 = Double.parseDouble(str2);

    // print double values
    System.out.println(num1);    // 23.0
    System.out.println(num2);    // 456.6
  }
}

In the above example, we have used the parseDouble() method of the Double class to convert the string variables into double.

Here, Double is a wrapper class in Java.

Note: The string variables should represent the number value. Otherwise, the compiler will throw an exception. For example,

class Main{
  public static void main(String[] args){

    // create a string variable
    String str1 = "Programiz";

    // convert string to double
    // using parseDouble()
    double num1 = Double.parseDouble(str1);

    // print double values
    System.out.println(num1);    // throws NumberFormatException
  }
}

Example 2: Java Program to Convert string to double using valueOf()

We can also convert the string variables into a double using the valueOf() method. For example,

class Main{
  public static void main(String[] args){

    // create string variables
    String str1 = "6143";
    String str2 = "21312";

    // convert String to double
    // using valueOf()
    double num1 = Double.valueOf(str1);
    double num2 = Double.valueOf(str2);

    // print double values
    System.out.println(num1);    // 6143.0
    System.out.println(num2);    // 21312.0
  }
}

In the above example, the valueOf() method of Double class converts the string values into the double.

Here, the valueOf() method actually returns an object of the Double class. However, the object is automatically converted into the primitive type. This is called unboxing in Java.

That is,

// valueOf() returns object of Double
// object is converted into double
double num1 = Double obj = Double.valueOf(str1);

Example 3: Java Program to Convert a String containing comma to double

class Main{
  public static void main(String[] args){

    // create string variables
    String str = "614,33";

    // replace the , with .
    str = str.replace(",", ".");

    // convert String to double
    // using valueOf()
    double value = Double.parseDouble(str);

    // print double value
    System.out.println(value);    // 614.33
  }
}

In the above example, we have created a string named str. Notice the line,

str = str.replace(",", ".");

Here, the replace() method replaces the comma present in the string with the dot character.

We then used the parseDouble() method to convert the string into double.