Java - Include decimal and preceding digits when setting length of double to be printed?

Question

I'm printing out a matrix, with each element having the same length printed on screen for easier reading.

If I do something like:

System.out.printf("%.16f", x);

then I get different lengths, depending on the preceding (whole) values:

x = 1;
x = 2.345;
x = 10;
x = 1243.5678;

gives the following outputs:

// 1.0000000000000000
// 2.3450000000000000
// 10.0000000000000000
// 1243.5678000000000000

which makes the matrix all messy. How can I limit the entire double - including the decimal and whole number - to a certain length? So, for the previous cases, the outputs would be:

// 1.0000000000000000
// 2.3450000000000000
// 10.000000000000000
// 1243.5678000000000

Edit #1

I don't want to just pad with zeros. Leading zeros are unattractive and can cause misreads. And even though I have %.16f right now, I may use less precision, and each digit will be significant (and non-zero).

Answer 1

One option is to chain two string formatting calls. The first call is:

String.format("%.16f", x)

This will give an arbitrary width string representation of a float with 16 places of precision. The next call should give a fixed width string of 18 characters which is right truncated, if necessary.

System.out.format("%18s : %s", String.format("%.16f", x));

Answer 2

There are different ways to format the output (but not exactly the same as your output):

1. Using printf method (assuming 21 digits width):

    System.out.printf("%21.16f%n", 1.0); System.out.printf("%21.16f%n", 2.345); System.out.printf("%21.16f%n", 10.0); System.out.printf("%21.16f", 1243.5678); 

   => output

1.0000000000000000
2.3450000000000000
10.0000000000000000
1243.5678000000000000

2. Use Apache Commons Lang library. Assuming you want to have 16 digits after the decimal point and 5 digits before it, the following might produce:

    System.out.println(StringUtils.rightPad(String.valueOf(1.0), 21, '0')); System.out.println(StringUtils.rightPad(String.valueOf(2.345), 21, '0')); System.out.println(StringUtils.rightPad(String.valueOf(10.0), 21, '0')); System.out.println(StringUtils.rightPad(String.valueOf(1243.5678), 21, '0')); 

the output:

1.0000000000000000000
2.3450000000000000000
10.000000000000000000
1243.5678000000000000

3. The other way is to use DecimalFormat :

    final String format = "00000.0000000000000000"; DecimalFormat formatter = new DecimalFormat(format); System.out.println(formatter.format(1.0)); System.out.println(formatter.format(2.345)); System.out.println(formatter.format(10.0)); System.out.println(formatter.format(1243.5678)); 

   and the ouput:

00001.0000000000000000
00002.3450000000000000
00010.0000000000000000
01243.5678000000000000

Answer 3

You should use BigDecimal for that.

Something like this:

BigDecimal db = new BigDecimal(d).setScale(6, BigDecimal.ROUND_HALF_UP);

You can read more about it here: .

You can convert the above Double to String and then convert the String to BigDecimal.

You can read this post for more details.