Java Rounding (Double)

Question

double y1 = 0;  
double y2 = 0;  
double i = 0.025;  
double n = 2;  
double h1 = 2000; 
double h2 = 4000; 

y1 = Math.pow((1 + i), n) * h1;
y2 = Math.pow((1 + i), n) * h2;
double result =  y1 + y2;
System.out.println(result);

I want the result as "6303.749999999999" but it gives me "6303.75". How can i solve it?

Possible duplicate of [How to round a number to n decimal places in Java](http://stackoverflow.com/questions/153724/how-to-round-a-number-to-n-decimal-places-in-java) — azurefrog, Oct 13 '15 at 14:25
Isn't that the same as wanting 0.999999999999 with code like: double a = 1? — ergonaut, Oct 13 '15 at 14:29

score 1 · Accepted Answer · answered Oct 13 '15 at 15:03

correct result should be (and it is) 6303.750000000000017069679003611781820568916563219777423023367655509563911228609889292329171439632773399353027343750000

Try to give a look at the BigDecimal class.

    BigDecimal i = new BigDecimal(0.025);
    int n = 2;
    BigDecimal h1 = new BigDecimal(2000);
    BigDecimal h2 = new BigDecimal(4000);

    BigDecimal y1 = ((BigDecimal.ONE.add(i)).pow(n)).multiply(h1);
    BigDecimal y2 = ((BigDecimal.ONE.add(i)).pow(n)).multiply(h2);
    BigDecimal result =  y1.add(y2);

    System.out.println(result.toEngineeringString());

score 0 · Answer 2 · answered Oct 13 '15 at 14:36

The problem is that you are calculating the value 6303.75. if you add a statement where you subtract the value 0.000000000001 from the variable result then you will get the expected value 6303.749999999999.

The below code changes demonstrate how you can instead calculate 6303.749999999999:

public static void main(String[] args){

    double y1 = 0;  
    double y2 = 0;  
    double i = 0.025;  
    double n = 2;  
    double h1 = 2000; 
    double h2 = 4000; 

    y1 = Math.pow((1 + i), n) * h1;
    y2 = Math.pow((1 + i), n) * h2;
    double result =  y1 + y2;
    result -= (double)0.000000000001; // this line is the key to calculating the expected result
    System.out.println(result);
}

Output:

6303.749999999999

Java Rounding (Double)

2 Answers2