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Tóm Tắt
Double.parseDouble()
We can parse String to double using
parseDouble()
method. String can start with “-” to denote negative number or “+” to denote positive number. Also any trailing 0s are removed from the double value. We can also have “d” as identifier that string is a double value. This method returns double primitive type. Below code snippet shows how to convert string to double using Double.parseDouble() method.String str = "+123.4500d"; double d = Double.parseDouble(str); // returns double primitive System.out.println(d); //-123.45, trailing 0s are removed 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
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Double.valueOf()
This method works almost similar as parseDouble() method, except that it returns Double object. Let’s see how to use this method to convert String to 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
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new Double(String s)
We can convert String to Double object through it’s constructor too. Also if we want double primitive type, then we can use
doubleValue()
method on it. Note that this constructor has been deprecated in Java 9, preferred approach is to useparseDouble()
orvalueOf()
methods.String str = "98.7"; double d = new Double(str).doubleValue(); //constructor deprecated in java 9 System.out.println(d); //98.7
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DecimalFormat parse()
This is useful to parse formatted string to double. For example, if String is “1,11,111.23d” then we can use DecimalFormat to parse this string to double as:
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 parse() method returns instance of
Number
, so we are callingdoubleValue()
to get the double primitive type from it. Also this method throwParseException
if the string is not properly formatted.
Java String to double conversion can be done by many ways. Today we will look into some common ways to convert java string to double primitive data type or Double object. Note that since java supports autoboxing, double primitive type and Double object can be used interchangeably without any issues.
Let’s look at all the different ways to convert string to double in java.