CODEWITHSUNDEEP
java
Amira
Amira

Reputation: 3270

Double minus operation result

I have a stupid question : 

String str0 = "245.00";
String str1 = "45.00";
Double str3 = Double.parseDouble(str0) - Double.parseDouble(str1); 
System.out.println(str3); =====> 200.0

Why it don't gives 200.00? (tested with Float too) And how to control number of digits after the comma?

Upvotes: 0

Views: 9988

Answers (3)

tar
tar

Reputation: 1568

When stored as a string, 10 is different than 10.0, which is also different than 10.00. When stored as a double, they may not be equal. Never trust two doubles to be ==/.equals() the same.

To print a double with a certain number of decimal places, use the printf method. For example:

String str0 = "245.00";
String str1 = "45.00";
Double str3 = Double.parseDouble(str0) - Double.parseDouble(str1); 

System.out.println(str3);        // 200.0
System.out.printf("%.2f", str3); // 200.00

Upvotes: 1

Rob Audenaerde
Rob Audenaerde

Reputation: 20029

To .0 comes from the default implementation of Java Double.toString().

To allow more control, use a Format. See here: NumberFormat api doc and here DecimalFormat tutorial

For simple formatting, you can also use String.format(), for example:

String.format("%02d", myNumber)

Or even print it directly using System.out.format

System.out.format("%.2f", myNumber);

Upvotes: 3

AurA
AurA

Reputation: 12363

This is not an answer but a general advice for doing floating point calculations.

You should use BigDecimal for calculations 

public class BigDecimalExample {

    public static void main(String args[]) throws IOException {

      //floating point calculation
      double amount1 = 2.15;
      double amount2 = 1.10;
      System.out.println("difference between 2.15 and 1.0 using double is: " + (amount1 - amount2));

      //Use BigDecimal for financial calculation
      BigDecimal amount3 = new BigDecimal("2.15");
      BigDecimal amount4 = new BigDecimal("1.10") ;
      System.out.println("difference between 2.15 and 1.0 using BigDecimal is: " + (amount3.subtract(amount4)));       
    }      
}

Output:

difference between 2.15 and 1.0 using double is: 1.0499999999999998

difference between 2.15 and 1.0 using BigDecmial is: 1.05

This answer is adapted from http://javarevisited.blogspot.in/2012/02/java-mistake-1-using-float-and-double.html

Also you can read a very good article on the need for BigDecimal http://www.javaworld.com/article/2071332/the-need-for-bigdecimal.html

Upvotes: 3

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