In this article, we will look at different ways to convert a String to a double value in java with example programs and explanation.

Method 1: Using parseDouble() method
java.lang.Double class has a parseDouble() method. This method takes a string argument and returns it as a double value.
parseDouble() is a static method which means that we do not need to create an object of Double class to invoke this method. Example,

String numStr = "2.5";
double num = Double.parseDouble(numStr);
System.out.println("Double value is: " + num);

This prints

Double value is: 2.5

String value should be parseable or convertible to double value, otherwise parseDouble() will throw a NumberFormatException.
Thus, below code will throw an exception.

String numStr = "two"; 
double num = Double.parseDouble(numStr);

Exception in thread “main” java.lang.NumberFormatException: For input string: “two”

Method 2: Using valueOf() method
valueOf() is also a static method in java.lang.Double class which accepts a String argument and returns its double equivalent value. Example,

String numStr = "2.5"; 
double num = Double.parseDouble(numStr); 
System.out.println("Double value is: " + num);

This method also throws a NumberFormatException, if the supplied string is not a parseable number.

Method 3: Using Double constructor
java.lang.Double class has a constructor which takes a string argument. This creates an object of Double class.
To get the value in double, use its doubleValue() method. Example,

String numStr = "2.5"; 
Double d = new Double(numStr);
double num = d.doubleValue();
System.out.println("Double value is: " + num);

This method is deprecated since java 9, its better to use parseDouble() or valueOf() methods.
Java doc states,

It is rarely appropriate to use this constructor. Use parseDouble(String) to convert a string to a double primitive, or use valueOf(String) to convert a string to a Double object.

Method 4: Using DecimalFormat
java.text.DecimalFormat class has a parse() method which takes a String argument and returns an object of type java.lang.Number.
Number is a super class of Double. Its doubleValue() returns a value of type double. Example,

String numStr = "2.5";
try {
   Number num = DecimalFormat.getInstance().parse(numStr);
   double doubleValue = num.doubleValue();
} catch (ParseException e) {
   e.printStackTrace();
}

To get an object of DecimalFormat, its static getInstance() method is used.
Note that parse() method of DecimalFormat throws java.text.ParseException, so we need to place it between try-catch block.
In one liner, this can be written as

double doubleValue = DecimalFormat.getInstance().parse(numStr).doubleValue();

Hope the article was helpful and informative.

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