How can I convert a Java String into a double data type?

2 years ago

Noah Thompson

3 minutes

There are several ways to convert a Java String to a double value. In this article, we will explore some commonly used methods for converting a Java String to either a double primitive type or a Double object. It is important to note that Java’s support for autoboxing allows for seamless interchangeability between the double primitive type and the Double object.

Double d1 = 10.25d;
//autoboxing from double to Double
double d = Double.valueOf(10.25); 
//unboxing from Double to double

How to convert a String to a Double in Java.

java convert string to double, java string to double

System.out.println(Double.parseDouble(“123.45001”)); //123.45001
System.out.println(Double.parseDouble(“123.45001d”)); //123.45001
System.out.println(Double.parseDouble(“123.45000”)); //123.45
System.out.println(Double.parseDouble(“123.45001D”)); //123.45001

Double.valueOf()
This method works in a similar way to the parseDouble() method, but it returns a Double object. The code snippet below shows how to use this method to convert a String to a Double object:
String str = “123.45”;
Double d = Double.valueOf(str); // returns Double object
System.out.println(d); //123.45

System.out.println(Double.valueOf(“123.45d”)); //123.45
System.out.println(Double.valueOf(“123.4500d”)); //123.45
System.out.println(Double.valueOf(“123.45D”)); //123.45

new Double(String s)
We can also convert a String to a Double object using its constructor. If we want a double primitive type, we can use the doubleValue() method on it. Note that this constructor has been deprecated in Java 9 and it is recommended to use the parseDouble() or valueOf() methods instead. The code snippet below demonstrates how to convert a String to a Double object using its constructor:
String str = “98.7”;
double d = new Double(str).doubleValue(); //constructor deprecated in java 9
System.out.println(d); //98.7

DecimalFormat parse()
This method is useful for parsing a formatted string to a double. For example, if the String is “1,11,111.23d”, we can use DecimalFormat to parse this string to a double as shown below:
String str = “1,11,111.23d”;
try {
double l = DecimalFormat.getNumberInstance().parse(str).doubleValue();
System.out.println(l); //111111.23
} catch (ParseException e) {
e.printStackTrace();
}

Note that the parse() method returns an instance of Number, so we are calling doubleValue() to get the double primitive type from it. This method also throws a ParseException if the string is not properly formatted.

The above information concludes the process of converting a string to a double in a Java program. You can refer to the Double API documentation for more details.