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Friday, 15 February 2013

JAVA: Parse String to Double

Paser String to Double:


You can parse a double value in string format to double in 4 ways.

  1. Double.valueof(String s) :  This method returns a double object containing the value invoked in it in string format.
    • It can trim white-space in start or end of the string argument, by using String.trim().
    • It throws NumberFormatException if the string argument is not in proper form.
  2.  Double.parseDouble(String s) : This method also returns a double instance containing the invoked string value.
    • It can also trim white space in start and end of the input value, using String.trim().
    • It also throws NumberFormatException if the string argument is not in proper form.
  3. new Double(String paramString) : You a also parse a string argument containing float value by invoking it on the constructor of the Class Double. its internally using the valueof(String s) method and returns a new Double instance containing the parsed double value. So it is also using
    String.trim() and throws NumberFormatException.
  4. Fourth one, the last one is the very important one, actually its been used by all the above 3 APIs. sun.misc.FloatingDecimal.readJavaFormatString(String paramString). Its the original method used to parse a String value to decimal value. This is the actual methods, which is trimming the white space of the string, using String.trim(). It returns value in FloatingDecimal instance, so you need to cast it to double by using doubleValue(), which is another method of Class FloatingDecimal.
Below is an example which explains the above discussion:

Code:


package com.interview.question.java;

public class PaserStringToDouble {

      /**
       *
       * Sample class that shows how to parse a String to double.
       *
       * @author http://interviewquestionjava.blogspot.com
       *
       */
      public static void main(String[] args) {
            // TODO Auto-generated method stub

            // set a decimal value in a string with
            // white space on both end.
            String strValue = " 12.329 ";

            // parse the string to double using
            //Double.valueof(String s)
            double dblValue = Double.valueOf(strValue);

            // parse the string to double using
            // Double.parseDouble(String s)
            double dblValue2 = Double.parseDouble(strValue);

            // parse the string to double using
      //Double(String paramString)
            Double dblValue3 = new Double(strValue);

            // parse the string to double using new
            // FloatingDecimal.readJavaFormatString
            //(String paramString)
            Double dblValue4 = new Double(sun.misc.FloatingDecimal
                        .readJavaFormatString(strValue).doubleValue());

            // printing the outputs
            System.out.println("dblValue: " + dblValue +
       "\ndblValue2: " + dblValue   + "\ndblValue3: " +
       dblValue3 + "\ndblValue4: " + dblValue4);

      }

}


Output:
dblValue: 12.329
dblValue2: 12.329
dblValue3: 12.329
dblValue4: 12.329

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