[java] How to use comparison operators like >, =, < on BigDecimal

I have a domain class with unitPrice set as BigDecimal data type. Now I am trying to create a method to compare price but it seems like I can't have comparison operators in BigDecimal data type. Do I have to change data type or is there other way around?

Use the compareTo method of BigDecimal :

public int compareTo(BigDecimal val) Compares this BigDecimal with the specified BigDecimal.

Returns:
-1, 0, or 1 as this BigDecimal is numerically less than, equal to, or greater than val.

You can use method named compareTo, x.compareTo(y). It will return 0 if x and y are equal, 1 if x is greater than y and -1 if x is smaller than y

This thread has plenty of answers stating that the BigDecimal.compareTo(BigDecimal) method is the one to use to compare BigDecimal instances. I just wanted to add for anymore not experienced with using the BigDecimal.compareTo(BigDecimal) method to be careful with how you are creating your BigDecimal instances. So, for example...

• new BigDecimal(0.8) will create a BigDecimal instance with a value which is not exactly 0.8 and which has a scale of 50+,
• new BigDecimal("0.8") will create a BigDecimal instance with a value which is exactly 0.8 and which has a scale of 1

... and the two will be deemed to be unequal according to the BigDecimal.compareTo(BigDecimal) method because their values are unequal when the scale is not limited to a few decimal places.

First of all, be careful to create your BigDecimal instances with the BigDecimal(String val) constructor or the BigDecimal.valueOf(double val) method rather than the BigDecimal(double val) constructor. Secondly, note that you can limit the scale of BigDecimal instances prior to comparing them by means of the BigDecimal.setScale(int newScale, RoundingMode roundingMode) method.

To be short:

firstBigDecimal.compareTo(secondBigDecimal) < 0 // "<"
firstBigDecimal.compareTo(secondBigDecimal) > 0 // ">"    
firstBigDecimal.compareTo(secondBigDecimal) == 0 // "=="  
firstBigDecimal.compareTo(secondBigDecimal) >= 0 // ">="    

Here is an example for all six boolean comparison operators (<, ==, >, >=, !=, <=):

BigDecimal big10 = new BigDecimal(10);
BigDecimal big20 = new BigDecimal(20);

System.out.println(big10.compareTo(big20) < -1);  // false
System.out.println(big10.compareTo(big20) <= -1); // true
System.out.println(big10.compareTo(big20) == -1); // true
System.out.println(big10.compareTo(big20) >= -1); // true
System.out.println(big10.compareTo(big20) > -1);  // false
System.out.println(big10.compareTo(big20) != -1); // false

System.out.println(big10.compareTo(big20) < 0);   // true
System.out.println(big10.compareTo(big20) <= 0);  // true
System.out.println(big10.compareTo(big20) == 0);  // false
System.out.println(big10.compareTo(big20) >= 0);  // false
System.out.println(big10.compareTo(big20) > 0);   // false
System.out.println(big10.compareTo(big20) != 0);  // true

System.out.println(big10.compareTo(big20) < 1);   // true
System.out.println(big10.compareTo(big20) <= 1);  // true
System.out.println(big10.compareTo(big20) == 1);  // false
System.out.println(big10.compareTo(big20) >= 1);  // false
System.out.println(big10.compareTo(big20) > 1);   // false
System.out.println(big10.compareTo(big20) != 1);  // true

BigDecimal isn't a primitive, so you cannot use the <, > operators. However, since it's a Comparable, you can use the compareTo(BigDecimal) to the same effect. E.g.:

public class Domain {
    private BigDecimal unitPrice;

    public boolean isCheaperThan(BigDecimal other) {
        return unitPirce.compareTo(other.unitPrice) < 0;
    }

    // etc...
}

Using com.ibm.etools.marshall.util.BigDecimalRange util class of IBM one can compare if BigDecimal in range.

boolean isCalculatedSumInRange = BigDecimalRange.isInRange(low, high, calculatedSum);