Correctly **compare float** or **compare double** is not only Java specific problem. It can be observed in almost all the programming languages today. In computer memory, floats and doubles are stored using IEEE 754 standard format. How the actual storage and conversion works, it is out of scope of this article.

For now, just understand that during computations and conversions, *minor rounding errors* can be introduced in these numbers. That’s why it is not advisable to simply rely on the *equality operators (==)* to **compare floating-point numbers**.

Let’s learn **how to compare float values in Java**.

Table of Contents 1. Simple comparison [Not recommended] 2. Threshold based comparison [Recommended] 3. Compare with BigDecimal [Recommended]

## 1. Compare double – Simple comparison [Not recommended]

First look at the simple comparison to understand what exactly is wrong with *comparing double with == operator*. In given program, I am creating same floating point number (i.e. `1.1`

) using two methods:

- Add
`.1`

, 11 times. - Multiply
`.1`

to 11.

In theory, both operations should produce the number `1.1`

. And when we compare the results of both methods, it should match.

private static void simpleFloatsComparison() { //Method 1 double f1 = .0; for (int i = 1; i <= 11; i++) { f1 += .1; } //Method 2 double f2 = .1 * 11; System.out.println("f1 = " + f1); System.out.println("f2 = " + f2); if (f1 == f2) System.out.println("f1 and f2 are equal\n"); else System.out.println("f1 and f2 are not equal\n"); }

Program Output.

f1 = 1.0999999999999999 f2 = 1.1 f1 and f2 are not equal

Look at the both values printed in console. `f1`

is computed to `1.0999999999999999`

. Its exactly the problem which rounding off causes internally. That’s why, **floating point comparison with '==' operator is not recommended**.

## 2. Compare double – Threshold based comparison [Recommended]

Now when we know the problem with equality operator, lets solve it. Using programming, we cannot change the way these floating point numbers are stored or computed. So we have to adapt a solution where we agree that a determine the differences in both values which we can tolerate and still consider the numbers equal. This agreed upon difference in values is called the **threshold** or **epsilon**.

So now to use ‘**threshold based floating point comparison**‘, we can use the `Math.abs()`

method to compute a difference between the two numbers and compare the difference to a threshold value.

private static void thresholdBasedFloatsComparison() { final double THRESHOLD = .0001; //Method 1 double f1 = .0; for (int i = 1; i <= 11; i++) { f1 += .1; } //Method 2 double f2 = .1 * 11; System.out.println("f1 = " + f1); System.out.println("f2 = " + f2); if (Math.abs(f1 - f2) < THRESHOLD) System.out.println("f1 and f2 are equal using threshold\n"); else System.out.println("f1 and f2 are not equal using threshold\n"); }

Program Output.

f1 = 1.0999999999999999 f2 = 1.1 f1 and f2 are equal using threshold

## 3. Compare double – Compare with BigDecimal [Recommended]

In `BigDecimal`

class, you can specify the **rounding mode** and **exact precision** which you want to use. Using the exact precision limit, rounding errors are mostly solved.

Best part is that `BigDecimal`

numbers are immutable i.e. if you create a `BigDecimal`

BD with value `"1.23"`

, that object will remain `"1.23"`

and can never be changed. This class provide many methods which can be used to do numerical operations on it’s value.

You can use it’s `compareTo()`

method to compare to `BigDecimal`

numbers. It ignore the scale while comparing.

a.compareTo(b);Method returns:

-1 – if a < b)

0 – if a == b

1 – if a > b

`equals()`

method to compare `BigDecimal`

instances. That is because this equals function will compare the scale. If the scale is different, `equals()`

will return false, even if they are the same number mathematically.Java program to compare double with `BigDecimal`

class.

private static void testBdEquality() { BigDecimal a = new BigDecimal("2.00"); BigDecimal b = new BigDecimal("2.0"); System.out.println(a.equals(b)); // false System.out.println(a.compareTo(b) == 0); // true }

Now just to verify, let’s solve out original problem using `BigDecimal`

class.

private static void bigDecimalComparison() { //Method 1 BigDecimal f1 = new BigDecimal("0.0"); BigDecimal pointOne = new BigDecimal("0.1"); for (int i = 1; i <= 11; i++) { f1 = f1.add(pointOne); } //Method 2 BigDecimal f2 = new BigDecimal("0.1"); BigDecimal eleven = new BigDecimal("11"); f2 = f2.multiply(eleven); System.out.println("f1 = " + f1); System.out.println("f2 = " + f2); if (f1.compareTo(f2) == 0) System.out.println("f1 and f2 are equal using BigDecimal\n"); else System.out.println("f1 and f2 are not equal using BigDecimal\n"); }

Program Output.

f1 = 1.1 f2 = 1.1 f1 and f2 are equal using BigDecimal

That’s all about **comparing floating point numbers in java**. Share your thoughts in comments section.

Happy Learning !!

sdm

This won’t work for infinity values. Here’s a test case to demonstrate this:

diwayou

public static boolean fuzzyEquals(double a, double b, double tolerance) {

MathPreconditions.checkNonNegative(“tolerance”, tolerance);

return Math.copySign(a – b, 1.0) <= tolerance

// copySign(x, 1.0) is a branch-free version of abs(x), but with different NaN semantics

|| (a == b) // needed to ensure that infinities equal themselves

|| (Double.isNaN(a) && Double.isNaN(b));

}

copy from guava DoubleMath

Srini

I tried this threshold value of floating number one but I am not getting both are same.

Please have a look and correct me.

Output:

Both are not equal

Akash

Its because you are using global variables. Try something like below

Sergey

Both methods are changing global var and are invoked twice. doubleOne results in 0.1*11+0.1*11, doubleTwo results in 0.1*11*11

You should:

Either don’t change global vars in the methods, that’s the best.

Invoke them once only, there is no need in invocation prior to if – remove those two method calls before the if block in main.