Round off Double to 2 decimal without changing the datatype

Question

double value1 = 1000
double value2 = 2563.59
System.out.println("value1 ="+String.format("%.2f",value1));
System.out.println("value2 ="String.format("%.2f",value2));

Output 
value1 = 1000.00
value2 = 2563.60

This returns 1000.00 and 2563.60 but the type of output changes to string.

I want 1000.00 and 2563.60 as the output without changing the datatype.

Can anyone help me?

The dtatype must be double itself

The output is printed, so doesn't matter the type if it's String, int, double .. why "not change datatype" ?^^ — azro, Aug 30 '17 at 07:05
@Viktor Mellgren Yes it can go through, but should return double — Fida, Aug 30 '17 at 08:02
@Fida but it has no sense, 2563.60 is not a double only a REPRESENTATION as a String, you can't, look at Sweeper answer, it's the nearer one — azro, Aug 30 '17 at 08:03
@azro what I am doing is getting the number from table and inserting it to excel using apache poi. There I want to calculate the sum.So I want to give the coming datas in the string to double so that they can get the sum — Fida, Aug 30 '17 at 08:34
@azro I knew its a representation, but I want 1000 as 1000.00 in double!! What should I do? — Fida, Aug 30 '17 at 08:35
@Fida you seems to not understand ^^ 1000.00 is a String, like answer given below — azro, Aug 30 '17 at 08:55
@Tom Actually I dont want to know how to round a number , but round a number without changing the datatype. thats what I want to know — Fida, Aug 30 '17 at 12:57
@Tom No in that answers all the type will be in the form of string — Fida, Aug 30 '17 at 12:59
The below answers all are giving me the datatype as string. Some are giving double but no .00 is there after whole numbers — Fida, Aug 30 '17 at 13:00

score 0 · Answer 1 · answered Aug 30 '17 at 07:04

Don't use String.format(..) if you don't want it to change to a string.

Please refer to Decimal Format

// 2 places of decimal
DecimalFormat formatter = new DecimalFormat( "#.00" );

System.out.println(formatter.format(1.23));    // 1.23
System.out.println(formatter.format(1));       // 1.00
System.out.println(formatter.format(1.234));   // 1.23

score 0 · Accepted Answer · answered Aug 30 '17 at 07:05

Note that double types store values, not strings. There are gonna be some cases where rounding it to 2 decimal places changes nothing. For example, the value 1. If you do a String.format on 1, it will become 1.00. However, 1 and 1.00 are the same value, so turning 1 to 2 decimal places makes it 1 again. double thinks that 1 and 1.00 are the same value (I mean, they really are, it's just formatted differently).

Also note that double values are inaccurate. It might appear as though it is 1.23 but in reality it might be something like 1.2300000000000001.

To correct a double to 2 d.p., all you have to do is to convert the formatted string back to a double:

String str = String.format("%.2f",value1));
double result = Double.parseDouble(str);

score 0 · Answer 3 · answered Aug 30 '17 at 07:09

0

why you are using string.format in first place?

DecimalFormat f = new DecimalFormat("##.00");
System.out.println(f.format(value1));

you need to import java.text.DecimalFormat; for this

answered Aug 30 '17 at 07:09

Omniverse10

134
2
15

Viktor Mellgren · Answer 4 · 2017-08-30T08:46:57.293

Using BigDecimal.setScale() and using rounding mode ceiling

    double value1 = 1000;
    double value2 = 2563.59;

    System.out.println("Before");
    System.out.println("value1 = " + value1);
    System.out.println("value2 = " + value2);

    value1 = BigDecimal.valueOf(value1).setScale(1, RoundingMode.CEILING).doubleValue();
    value2 = BigDecimal.valueOf(value2).setScale(1, RoundingMode.CEILING).doubleValue();

    System.out.println("After");
    System.out.println("value1 = " + value1);
    System.out.println("value2 = " + value2);

score 0 · Answer 5 · answered Aug 30 '17 at 11:50

In anything that uses limited-precision, binary floating-point numbers -- which is the default for Java and most programming languages -- the concept "number of decimal places" only ever applies to display. The internal binary representation has no concept of "decimal places" because the data is not decimal.

Consequently, the number of decimal places applies only to how data is displayed, and it is irrelevant what data types may be used to do the display.

When questions arise about rounding decimal numbers, it's often because the programmer has not fully understood how float-point math works.

Round off Double to 2 decimal without changing the datatype

5 Answers5