Java – How does BigDecimal compare, but approximately?

I have this code :

BigDecimal d = ...;
if (d.compareTo(Expression.PI) == 0) {
    do something
}

where Expression.PI is pi rounded to the 100th decimal place.

But I don’t need to compare if d equals pi to up to 100 decimal places, but just say up to 20 decimal places. In other words, how can you tell if d is approximately equal to pi?

I tried

Expression.PI.setScale(20, RoundingMode.HALF_UP).compareTo(d.setScale(20, RoundingMode.HALF_UP)) == 0;

and

Expression.PI.setScale(20, RoundingMode.HALF_UP).compareTo(d) == 0;

But neither of these seems to work. What am I doing wrong here?

As lucasvw mentioned in the comment, I think you’ve done it correctly and there must be something wrong with your “d” value. This is a test class that shows the correct results.

import java.math.BigDecimal;
import java.math.RoundingMode;

public class BigDecimalTest {

public static void main(String args[]) {
    BigDecimal PI = new BigDecimal("3.14159265358979323846264338327950288419");
    BigDecimal otherValue = new BigDecimal("3.14159");

boolean test = PI.setScale(5, RoundingMode.HALF_UP).compareTo(otherValue) == 0;

System.out.println("compareTo: " + test);
}
}