How to check if BigDecimal variable == 0 in java?

Alternatively, I think it is worth mentioning that the behavior of equals and compareTo methods in the class BigDecimal are not consistent with each other.

This basically means that:

BigDecimal someValue = new BigDecimal("0.00");
System.out.println(someValue.compareTo(BigDecimal.ZERO) == 0); // true
System.out.println(someValue.equals(BigDecimal.ZERO)); // false

Therefore, you have to be very careful with the scale in your someValue variable, otherwise you would get unexpected results.

Alternatively, signum() can be used:

if (price.signum() == 0) {
    return true;
}

There is a constant that you can check against:

someBigDecimal.compareTo(BigDecimal.ZERO) == 0

Use compareTo(BigDecimal.ZERO) instead of equals():

if (price.compareTo(BigDecimal.ZERO) == 0) // see below

Comparing with the BigDecimal constant BigDecimal.ZERO avoids having to construct a new BigDecimal(0) every execution.

FYI, BigDecimal also has constants BigDecimal.ONE and BigDecimal.TEN for your convenience.

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Note!

The reason you can't use BigDecimal#equals() is that it takes scale into consideration:

new BigDecimal("0").equals(BigDecimal.ZERO) // true
new BigDecimal("0.00").equals(BigDecimal.ZERO) // false!

so it's unsuitable for a purely numeric comparison. However, BigDecimal.compareTo() doesn't consider scale when comparing:

new BigDecimal("0").compareTo(BigDecimal.ZERO) == 0 // true
new BigDecimal("0.00").compareTo(BigDecimal.ZERO) == 0 // true