Best Way to Format a Double Value to 2 Decimal Places

Best way to Format a Double value to 2 Decimal places

No, there is no better way.

Actually you have an error in your pattern. What you want is:

DecimalFormat df = new DecimalFormat("#.00"); 

Note the "00", meaning exactly two decimal places.

If you use "#.##" (# means "optional" digit), it will drop trailing zeroes - ie new DecimalFormat("#.##").format(3.0d); prints just "3", not "3.00".

Round a double to 2 decimal places

Here's an utility that rounds (instead of truncating) a double to specified number of decimal places.

For example:

round(200.3456, 2); // returns 200.35

Original version; watch out with this

public static double round(double value, int places) {
    if (places < 0) throw new IllegalArgumentException();

    long factor = (long) Math.pow(10, places);
    value = value * factor;
    long tmp = Math.round(value);
    return (double) tmp / factor;
}

This breaks down badly in corner cases with either a very high number of decimal places (e.g. round(1000.0d, 17)) or large integer part (e.g. round(90080070060.1d, 9)). Thanks to Sloin for pointing this out.

I've been using the above to round "not-too-big" doubles to 2 or 3 decimal places happily for years (for example to clean up time in seconds for logging purposes: 27.987654321987 -> 27.99). But I guess it's best to avoid it, since more reliable ways are readily available, with cleaner code too.

So, use this instead

(Adapted from this answer by Louis Wasserman and this one by Sean Owen.)

public static double round(double value, int places) {
    if (places < 0) throw new IllegalArgumentException();

    BigDecimal bd = BigDecimal.valueOf(value);
    bd = bd.setScale(places, RoundingMode.HALF_UP);
    return bd.doubleValue();
}

Note that HALF_UP is the rounding mode "commonly taught at school". Peruse the RoundingMode documentation, if you suspect you need something else such as Bankers’ Rounding.

Of course, if you prefer, you can inline the above into a one-liner:

new BigDecimal(value).setScale(places, RoundingMode.HALF_UP).doubleValue()

And in every case

Always remember that floating point representations using float and double are inexact.
For example, consider these expressions:

999199.1231231235 == 999199.1231231236 // true
1.03 - 0.41 // 0.6200000000000001

For exactness, you want to use BigDecimal. And while at it, use the constructor that takes a String, never the one taking double. For instance, try executing this:

System.out.println(new BigDecimal(1.03).subtract(new BigDecimal(0.41)));
System.out.println(new BigDecimal("1.03").subtract(new BigDecimal("0.41")));

Some excellent further reading on the topic:

• Item 48: "Avoid float and double if exact answers are required" in Effective Java (2nd ed) by Joshua Bloch
• What Every Programmer Should Know About Floating-Point Arithmetic

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If you wanted String formatting instead of (or in addition to) strictly rounding numbers, see the other answers.

Specifically, note that round(200, 0) returns 200.0. If you want to output "200.00", you should first round and then format the result for output (which is perfectly explained in Jesper's answer).

How to print a float with 2 decimal places in Java?

You can use the printf method, like so:

System.out.printf("%.2f", val);

In short, the %.2f syntax tells Java to return your variable (val) with 2 decimal places (.2) in decimal representation of a floating-point number (f) from the start of the format specifier (%).

There are other conversion characters you can use besides f:

• d: decimal integer
• o: octal integer
• e: floating-point in scientific notation

Round up double to 2 decimal places

Use a format string to round up to two decimal places and convert the double to a String:

let currentRatio = Double (rxCurrentTextField.text!)! / Double (txCurrentTextField.text!)!
railRatioLabelField.text! = String(format: "%.2f", currentRatio)

Example:

let myDouble = 3.141
let doubleStr = String(format: "%.2f", myDouble) // "3.14"

If you want to round up your last decimal place, you could do something like this (thanks Phoen1xUK):

let myDouble = 3.141
let doubleStr = String(format: "%.2f", ceil(myDouble*100)/100) // "3.15"

Formatting a double to two decimal places

string.Format will not change the original value, but it will return a formatted string. For example:

Console.WriteLine("Earnings this week: {0:0.00}", answer);

Note: Console.WriteLine allows inline string formatting. The above is equivalent to:

Console.WriteLine("Earnings this week: " + string.Format("{0:0.00}", answer));

Rounding a double value to x number of decimal places in swift

You can use Swift's round function to accomplish this.

To round a Double with 3 digits precision, first multiply it by 1000, round it and divide the rounded result by 1000:

let x = 1.23556789
let y = Double(round(1000 * x) / 1000)
print(y) /// 1.236

Unlike any kind of printf(...) or String(format: ...) solutions, the result of this operation is still of type Double.

EDIT:

Regarding the comments that it sometimes does not work, please read this: What Every Programmer Should Know About Floating-Point Arithmetic

How to round the double value to 2 decimal points?

There's no difference in internal representation between 2 and 2.00. You can use Math.round to round a value to the nearest integer - to make that round to 2 decimal places you could multiply by 100, round, and then divide by 100, but you shouldn't expect the result to be exactly 2dps, due to the nature of binary floating point arithmetic.

If you're only interested in formatting a value to two decimal places, look at DecimalFormat - if you're interested in a number of decimal places while calculating you should really be using BigDecimal. That way you'll know that you really are dealing with decimal digits, rather than "the nearest available double value".

Another option you may want to consider if you're always dealing with two decimal places is to store the value as a long or BigInteger, knowing that it's exactly 100 times the "real" value - effectively storing cents instead of dollars, for example.

How do I display a decimal value to 2 decimal places?

decimalVar.ToString("#.##"); // returns ".5" when decimalVar == 0.5m

or

decimalVar.ToString("0.##"); // returns "0.5"  when decimalVar == 0.5m

or

decimalVar.ToString("0.00"); // returns "0.50"  when decimalVar == 0.5m

Formatting Double to exactly 2 Decimal places IF required

This is definitely a bit of a hack, but I don't know if the DecimalFormat syntax allows for anything better. This simply checks to see if the number is real, and formats based on the spec you asked for.

    double number = 25000.5;
    DecimalFormat df;

    if(number%1==0)
         df = new DecimalFormat("##,###");
    else
        df = new DecimalFormat("##,###.00");

    System.out.println(df.format(number));

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