CODEWITHSUNDEEP
java
kakoli
kakoli

Reputation: 447

What is good way to check equality between 2 doubles in Java

For Double/Float, there are some rounding errors and loss of precision when converting from decimal to binary representation. For example, setting float to "6.1" and then printing it out again, you may get a reported value of something like "6.099999904632568359375". Which is the better option for checking equality of 2 Double objects : Using BigDecimal or (Math.abs(double1 - double2) < epsilon)

Upvotes: 9

Views: 18694

Answers (7)

dobrivoje
dobrivoje

Reputation: 982

here is an example for jdk >= 21 :

record MeasurementDetails(LocalDateTime eventDate, double temp, double hum) {}
record Measurement(MeasurementDetails measurementDetails, double difference) {}

var res = new ArrayList<Measurement>();
// add elements to the "res" list...

var m1 = res.stream().findFirst().orElseThrow(); // first element
var m2 = res.stream().skip(1).findFirst().orElseThrow(); // second
var m3 = res.stream().skip(2).findFirst().orElseThrow(); // third

// equality is tolerated on 10^-6 
assertThat(m1.difference()).isCloseTo(-0.2, Offset.offset(0.000001));
assertThat(m2.difference()).isCloseTo(-0.4, Offset.offset(0.000001));
assertThat(m3.difference()).isCloseTo(0, Offset.offset(0.000001));

Upvotes: 0

Chase
Chase

Reputation: 104

If you can use a library, you can use Apache Commons Math, there is a Precision class. Works the same way as previous answers.

boolean isEqual = Precision.equals(double x, double y, double eps);

link to javadoc

Upvotes: 1

Constantin-Alexandru Tabacu
Constantin-Alexandru Tabacu

Reputation: 61

With Guava, you have:

DoubleMath.fuzzyEquals(double a, double b, double tolerance)

and

DoubleMath.fuzzyCompare(double a, double b, double tolerance)

They are easier to use and more correct than writing "Math.abs(a-b) <= EPSILON". They cover the cases of Double.NaN and the infinities.

Upvotes: 6

Ace Zachary
Ace Zachary

Reputation: 449

It would be different based on the level of accuracy needed. But may be take a look at Java.lang.Double.equals() method.

Upvotes: 0

awiebe
awiebe

Reputation: 3836

Floating point numbers have what is called an epsilon tolerance, the minimum representable value. To compare floats check their difference is within tolerance.

Math.abs(a-b) <= EPSILON

Of course if you happen to be working with a number that is too big to fit in a double, you should use the big number variant. EPSILON is some tolerance several orders greater than Double.MIN_VALUE, but sufficiently small that the variance is negligible.

Upvotes: 0

Mithilesh Gupta
Mithilesh Gupta

Reputation: 2930

If you want to test equality you can use Double.compare() or BigDecimal.

If you need want approximate equality then Math.abs(d1-d2) < epsilon

Upvotes: 0

Burkhard
Burkhard

Reputation: 14738

It depends on your usecase. If you work with currency, go for BigDecimal. Otherwise if you can live with approximations use Math.abs(double1 - double2) < epsilon

Upvotes: 5

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