Convert double to BigDecimal and set BigDecimal Pr

Question

In Java, I want to take a double value and convert it to a BigDecimal and print out its String value to a certain precision.

import java.math.BigDecimal;
public class Main {
    public static void main(String[] args) {
        double d=-.00012;
        System.out.println(d+""); //This prints -1.2E-4

        double c=47.48000;
        BigDecimal b = new BigDecimal(c);
        System.out.println(b.toString()); 
        //This prints 47.47999999999999687361196265555918216705322265625 
    }
}

It prints this huge thing:

47.47999999999999687361196265555918216705322265625

and not

47.48

The reason I'm doing the BigDecimal conversion is sometimes the double value will contain a lot of decimal places (i.e. -.000012) and the when converting the double to a String will produce scientific notation -1.2E-4. I want to store the String value in non-scientific notation.

I want to have BigDecimal always have two units of precision like this: "47.48". Can BigDecimal restrict precision on conversion to string?

Answer 1

You want to try String.format("%f", d), which will print your double in decimal notation. Don't use BigDecimal at all.

Regarding the precision issue: You are first storing 47.48 in the double c, then making a new BigDecimal from that double. The loss of precision is in assigning to c. You could do

BigDecimal b = new BigDecimal("47.48")

to avoid losing any precision.

Answer 2

The String.format syntax helps us convert doubles and BigDecimals to strings of whatever precision.

This java code:

double dennis = 0.00000008880000d;
System.out.println(dennis);
System.out.println(String.format("%.7f", dennis));
System.out.println(String.format("%.9f", new BigDecimal(dennis)));
System.out.println(String.format("%.19f", new BigDecimal(dennis)));

Prints:

8.88E-8
0.0000001
0.000000089
0.0000000888000000000