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

I have the following code in Java;

BigDecimal price; // assigned elsewhere

if (price.compareTo(new BigDecimal("0.00")) == 0) {
	return true;
}

What is the best way to write the if condition?

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.

---

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

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

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.

I usually use the following:

if (selectPrice.compareTo(BigDecimal.ZERO) == 0) { ... }

You would want to use equals() since they are objects, and utilize the built in ZERO instance:

if (selectPrice.equals(BigDecimal.ZERO))

Note that .equals() takes scale into account, so unless selectPrice is the same scale (0) as .ZERO then this will return false.

To take scale out of the equation as it were:

if (selectPrice.compareTo(BigDecimal.ZERO) == 0)

I should note that for certain mathematical situations, 0.00 != 0, which is why I imagine .equals() takes the scale into account. 0.00 gives precision to the hundredths place, whereas 0 is not that precise. Depending on the situation you may want to stick with .equals().

GriffeyDog is definitely correct:

Code:

BigDecimal myBigDecimal = new BigDecimal("00000000.000000");
System.out.println("bestPriceBigDecimal=" + myBigDecimal);
System.out.println("BigDecimal.valueOf(0.000000)=" + BigDecimal.valueOf(0.000000));
System.out.println(" equals=" + myBigDecimal.equals(BigDecimal.ZERO));
System.out.println("compare=" + (0 == myBigDecimal.compareTo(BigDecimal.ZERO)));

Results:

myBigDecimal=0.000000
BigDecimal.valueOf(0.000000)=0.0
 equals=false
compare=true

While I understand the advantages of the BigDecimal compare, I would not consider it an intuitive construct (like the ==, <, >, <=, >= operators are). When you are holding a million things (ok, seven things) in your head, then anything you can reduce your cognitive load is a good thing. So I built some useful convenience functions:

public static boolean equalsZero(BigDecimal x) {
	return (0 == x.compareTo(BigDecimal.ZERO));
}
public static boolean equals(BigDecimal x, BigDecimal y) {
	return (0 == x.compareTo(y));
}
public static boolean lessThan(BigDecimal x, BigDecimal y) {
	return (-1 == x.compareTo(y));
}
public static boolean lessThanOrEquals(BigDecimal x, BigDecimal y) {
	return (x.compareTo(y) <= 0);
}
public static boolean greaterThan(BigDecimal x, BigDecimal y) {
	return (1 == x.compareTo(y));
}
public static boolean greaterThanOrEquals(BigDecimal x, BigDecimal y) {
	return (x.compareTo(y) >= 0);
}

Here is how to use them:

	System.out.println("Starting main Utils");
	BigDecimal bigDecimal0 = new BigDecimal(00000.00);
	BigDecimal bigDecimal2 = new BigDecimal(2);
	BigDecimal bigDecimal4 = new BigDecimal(4);  
	BigDecimal bigDecimal20 = new BigDecimal(2.000);
	System.out.println("Positive cases:");
	System.out.println("bigDecimal0=" + bigDecimal0 + " == zero is " + Utils.equalsZero(bigDecimal0));
	System.out.println("bigDecimal2=" + bigDecimal2 + " <  bigDecimal4=" + bigDecimal4 + " is " + Utils.lessThan(bigDecimal2, bigDecimal4));
	System.out.println("bigDecimal2=" + bigDecimal2 + " == bigDecimal20=" + bigDecimal20 + " is " + Utils.equals(bigDecimal2, bigDecimal20));
	System.out.println("bigDecimal2=" + bigDecimal2 + " <= bigDecimal20=" + bigDecimal20 + " is " + Utils.equals(bigDecimal2, bigDecimal20));
	System.out.println("bigDecimal2=" + bigDecimal2 + " <= bigDecimal4=" + bigDecimal4 + " is " + Utils.lessThanOrEquals(bigDecimal2, bigDecimal4));
	System.out.println("bigDecimal4=" + bigDecimal4 + " >  bigDecimal2=" + bigDecimal2 + " is " + Utils.greaterThan(bigDecimal4, bigDecimal2));
	System.out.println("bigDecimal4=" + bigDecimal4 + " >= bigDecimal2=" + bigDecimal2 + " is " + Utils.greaterThanOrEquals(bigDecimal4, bigDecimal2));
	System.out.println("bigDecimal2=" + bigDecimal2 + " >= bigDecimal20=" + bigDecimal20 + " is " + Utils.greaterThanOrEquals(bigDecimal2, bigDecimal20));
	System.out.println("Negative cases:");
	System.out.println("bigDecimal2=" + bigDecimal2 + " == zero is " + Utils.equalsZero(bigDecimal2));
	System.out.println("bigDecimal2=" + bigDecimal2 + " == bigDecimal4=" + bigDecimal4 + " is " + Utils.equals(bigDecimal2, bigDecimal4));
	System.out.println("bigDecimal4=" + bigDecimal4 + " <  bigDecimal2=" + bigDecimal2 + " is " + Utils.lessThan(bigDecimal4, bigDecimal2));
	System.out.println("bigDecimal4=" + bigDecimal4 + " <= bigDecimal2=" + bigDecimal2 + " is " + Utils.lessThanOrEquals(bigDecimal4, bigDecimal2));
	System.out.println("bigDecimal2=" + bigDecimal2 + " >  bigDecimal4=" + bigDecimal4 + " is " + Utils.greaterThan(bigDecimal2, bigDecimal4));
	System.out.println("bigDecimal2=" + bigDecimal2 + " >= bigDecimal4=" + bigDecimal4 + " is " + Utils.greaterThanOrEquals(bigDecimal2, bigDecimal4));

The results look like this:

Positive cases:
bigDecimal0=0 == zero is true
bigDecimal2=2 <  bigDecimal4=4 is true
bigDecimal2=2 == bigDecimal20=2 is true
bigDecimal2=2 <= bigDecimal20=2 is true
bigDecimal2=2 <= bigDecimal4=4 is true
bigDecimal4=4 >  bigDecimal2=2 is true
bigDecimal4=4 >= bigDecimal2=2 is true
bigDecimal2=2 >= bigDecimal20=2 is true
Negative cases:
bigDecimal2=2 == zero is false
bigDecimal2=2 == bigDecimal4=4 is false
bigDecimal4=4 <  bigDecimal2=2 is false
bigDecimal4=4 <= bigDecimal2=2 is false
bigDecimal2=2 >  bigDecimal4=4 is false
bigDecimal2=2 >= bigDecimal4=4 is false

A simple and better way for your exemple is:

BigDecimal price;

if(BigDecimal.ZERO.compareTo(price) == 0){
    
   //Returns TRUE

}

Just want to share here some helpful extensions for kotlin

fun BigDecimal.isZero() = compareTo(BigDecimal.ZERO) == 0
fun BigDecimal.isOne() = compareTo(BigDecimal.ONE) == 0
fun BigDecimal.isTen() = compareTo(BigDecimal.TEN) == 0

if(price.floatValue() == 0){
   return true; //works for 0\0.0
}

BigDecimal.ZERO.setScale(2).equals(new BigDecimal("0.00"));

There is a static constant that represents 0:

BigDecimal.ZERO.equals(selectPrice)

You should do this instead of:

selectPrice.equals(BigDecimal.ZERO)

in order to avoid the case where selectPrice is null.