How To Convert String To Double In Java

When converting from string to double, it is important that the string contains a valid double value. However, to convert from string to int there are several things to consider.

How to Convert String To A Simple Double

The class Double contains a static method, which can be used to achieve exactly that:

Double.parseDouble(String s)

This method takes a string that must be formatted correctly. This means that it consists exclusively of digits, separated by a maximum of one dot. Only one plus or minus character is allowed at the beginning.

Double.parseDouble("");       // Error - no numbers
Double.parseDouble("1");      // correct
Double.parseDouble("1.1");    // correct
Double.parseDouble(".1");     // correct
Double.parseDouble(".");      // Error - no numbers
Double.parseDouble("-1");     // correct
Double.parseDouble("+1");     // correct
Double.parseDouble("1.1");    // correct
Double.parseDouble(" 1");     // correct - Whitespaces at start and end are ignored
Double.parseDouble("1,1");    // Error - Comma not allowed
Double.parseDouble("1_000");  // Error - Separator not allowed

A string containing illegal characters causes a java.lang.NumberFormatException.


How to Convert String To Double Object

To convert a string into Double class object, there is the static method Double.valueOf(String s):

Double i = Double.valueOf("1");

Of course you can also assign the result of Double.parseDouble() to a double object by autoboxing:

Double i = Double.parseDouble("1");
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