How to Convert Double to String to Double in Java Program with Example

Many scenarios come in day to day Java programming when we need to convert a Double value to String or vice versa. In my earlier article we have seen how to convert String to Integer and in this article, we will first see how to convert double to String and the later opposite of  that from String to double. One important thing to note is Autoboxing which automatically converts primitive type to Object type and only available from Java 5 onwards. This conversion example assumes the code is running above Java 5 version and actually tested in JDK 1.6, which makes it unable to pass Double object when the method is expecting double primitive value likeString.valueOf(double d) which expect a double value.

In case, you want to use these example of String to float prior to Java 5 you probably want to change a bit and use intValue(), doubleValue() method to convert primitive from Object type.

Converting String to Double in Java

There are at least three ways to convert a String, representing double value, into a Double Object. There could be more ways to do the same , Please let us know if you know any other method of conversion which is not listed here.

1) The first way of converting a String to Double has just created a new Double object. Double has a constructor which expects a String value and it return a Double object with same value.

String toBeDouble = "200.20";

Double fromString = new Double(toBeDouble);

Beware of NumberFormatException which will occur if the String is not representing a valid Double value.

2) The second way of String to double conversion is by using parseDouble(String str) from Double class. by far this is my preferred method because it's more readable and standard way of converting a string value to double. here is an example :

Double doubleString = Double.parseDouble(toBeDouble);

Again you need to take care of NumberFormatException which can occur while converting an invalid double string to double object.

3) A third way to change String into Double is by using Double.valueOf(String str) method. Just pass your double string into this method and it will convert to equivalent Double value.

Double doubleStr = Double.valueOf(toBeDouble);

This method can also throw NumberFormatException if String is null or not convertible to double. though Whitespace is ignored by Java.

Convert Double to String in Java Program

Converting Double to String in Java

As with above examples, there are multiple ways to convert a Double object into String. In this example of converting double to String, we will see at least four ways of doing same. this is rather much easier than the opposite.

1) The first way to convert Double to string is using concatenation operator "+" which produce a new string. This is by far the simplest way of converting a double object to a string.

Double toBeString = 400.40;

String fromDouble = "" + toBeString;

2) The second way of double to String conversion is by using String.valueOf(double d) method , which takes a double value as an argument and returns it in a form of String literal. here is an example of converting double to String using valueOf() method.

String strDouble = String.valueOf(toBeString);

3) A third way to convert double into String is by using toString() method of Double Class, which is essentially the same way used in a first way because concatenation operator internally calls toString() method of an object to get its string value.

String stringDouble = toBeString.toString();

4) The fourth way is rather more a flexible way of getting String from Double. it uses String.format() method and returns a formatted string so you can control the precision level and get a String up to two decimal points or three decimal points based on your requirement.

String convertedString = String.format("%.3f", toBeString);

This convertedString contains double value up to 3 decimal points. "f" is used to format floating point numbers. As you may have noticed we are passing the Double object to methods which are expecting double primitive value and that is only possible due to autoboxing. if you are running below Java 5 use intValue() doubleValue() methods to get value in primitive format.

These are some basic ways to change any String into Double wrapper Class and vice versa. Please let us know if you are familiar with any other utility or method or doing the same thing with less hassle may be like overriding equals using EqualsBuilder and HashCodeBuilder.

Further Learning

Complete Java Masterclass

Java Fundamentals: The Java Language

Java In-Depth: Become a Complete Java Engineer!

Some of my other Java articles:

How to Convert String to Date in Java

How to Set Path for Java in Windows XP

How to Set ClassPath for Java in Windows

What is PolyMorphism in Java

What is abstraction in Java with Example

How to Solve Java.lang.OutOfMemoryError: Java Heap Space

How to Solve UnSupportedClassVersionError in Java