How to keep n decimal places in Java

Question

Hi All it might be a trivial question but as for now I could not find any solution.So asking for your help!

What I am trying to get is a specific encoding table that looks like this:

0.000
0.100
0.200

I need to keep track of zeroes as I will use them to reconstruct a part of an specific array. Original loop that was creating those numbers is:

for(int k=0;k<m_0;k++){
    for(int l=0;l<m_1;l++){
        for(int a=0;a<a1;a++){
            
            Y[x-1]=0.1*k+0.01*l+0.001*a;
            x++;
            
        }
        
    }
    
}

Problem! I could not fix zeros after decimal place and rather then getting table described above I am getting following:

0.0
0.1
0.2

As a solution I have tried to use BigDecimal and DecimalFormat but no success. Any suggestions?

UPD Few words what I am trying to do. I am encoding specific array to array and back index correspondence. For example 0.100 will be decomposed into 1 and 0 and 0 and used as array index labeling like:

Array1[Method(1,0,0,Y(i)][Method(1,0,0,Y(i))]=Array2[1][0][0]

So that I need an output suitable for assigning array index and string will not do the deal.

The DecimalFormat class seems the way to go as described below. Could you post what you're trying to do so that we can see why it failed? — Jeff Wang, Apr 02 '14 at 23:07
Hi Jeff, I have described in the Update section what I am trying to achieve. I am trying to get later from those .100 array elements like 1,0 and 0. That is why floating zero is crucial. — madbitloman, Apr 03 '14 at 03:55

score 8 · Accepted Answer · answered Apr 02 '14 at 22:57

8

The DecimalFormat class is the correct place to look. You just need the correct format.

DecimalFormat df = new DecimalFormat("0.000");
System.out.println(df.format(0.1));

Output:

0.100

answered Apr 02 '14 at 22:57

rgettman

176,041
30
275
357

score 2 · Answer 2 · answered Apr 02 '14 at 23:11

As an alternative to the DecimalFormat class, I would like to propose the following (which I use quite regularly):

Step 1: Create a function that allows me to specify the number of units to keep. Here is a copy of this function.

public static String format(Number n) {
        NumberFormat format = DecimalFormat.getInstance();
        format.setRoundingMode(RoundingMode.FLOOR);
        format.setMinimumFractionDigits(0);
        format.setMaximumFractionDigits(2);
        return format.format(n);
    }

Step 2: Call the function whenever you have any output to format. Below is a simple example using this function to set the appropriate decimal place length:

System.out.println("Based on this, the wind chill index was calculated to be " + format(chill));

Note that you could simply change the line:

format.setMaximumFractionDigits(2);

to

format.setMaximumFractionDigits(n);

depending on your desired decimal length.

score 2 · Answer 3 · answered Apr 02 '14 at 23:42

2

When you are printing the numbers, you can use this:

System.out.format("%.3f", yourDecimalNumber);

answered Apr 02 '14 at 23:42

adam

240
1
7

How to keep n decimal places in Java

3 Answers3